3d digital documentation, assessment, and damage quantification of the al-deir monument in the...
DESCRIPTION
The rock-cut monuments in the ancient city of Petra in Jordan form an outstanding tangible heritage site. Unfortunately, this important part of the world’s cultural heritage is gradually being diminished due to weathering and erosion problems. In this research, an approach combining in situ surveying and laboratory analysis is applied in order to provide sufficient and comprehensive data regarding the documentation and evaluation of the status of the Al-Deir monument in Petra. The purpose was not only to quantify the damage, but also to make a first step towards creating a 3D monitoring programme of the deterioration rate. The approach presents a correlation study between the environmental condition and the surface weathering damage, using 2D mapping of the weathering form and accurate 3D realistic modelling from laser scanning and digital photogrammetry. The2D mapping provides detailed weathering damage information for the entire stone surface of the monument, whereas the 3D modelling provides information on the spatial distribution and texture of the damage. Additionally, the 3D digital model can provide reference data as an exact guide to the restoration needed. In order to support the visual presentation of 3D surface details, a hybrid approach combining data from laser scanning and digital imagery was developed.Studies of stone texture and spatial distribution of soluble salts werecarried out at the monument in order to explain the mechanism of the weathering problem. Relative humidity, temperature, and wind are the main factors in the salt damage process. In order to study the effect of these conditions in the salt crystallization process a series of fieldwork 3D DIGITAL DOCUMENTATION IN PETRA 125investigations and laboratory work were undertaken. The results show that visible zoning of weathering damage is correlated to different salt concentrations.TRANSCRIPT
© W. S. Maney & Son Ltd 2010 DOI 10.1179/175355210X12792909186412
conservation and mgmt of arch. sites, Vol. 12 No. 2, May, 2010, 124–45
3D Digital Documentation, Assessment, and Damage Quantifi cation of the Al-Deir Monument in the Ancient City of Petra, JordanYahya Alshawabkeh and Fadi Bal’awi The Hashemite University, Jordan
Norbert HaalaInstitute for Photogrammetry (ifp), University of Stuttgart, Germany
The rock-cut monuments in the ancient city of Petra in Jordan form an out-standing tangible heritage site. Unfortunately, this important part of the world’s cultural heritage is gradually being diminished due to weathering and erosion problems. In this research, an approach combining in situ surveying and laboratory analysis is applied in order to provide suffi cient and comprehensive data regarding the documentation and evaluation of the status of the Al-Deir monument in Petra. The purpose was not only to quantify the damage, but also to make a fi rst step towards creating a 3D monitoring programme of the deterioration rate. The approach presents a correlation study between the environmental condition and the surface weathering damage, using 2D mapping of the weathering form and accurate 3D realistic modelling from laser scanning and digital photogrammetry. The 2D mapping provides detailed weathering damage information for the entire stone surface of the monument, whereas the 3D modelling provides infor-mation on the spatial distribution and texture of the damage. Additionally, the 3D digital model can provide reference data as an exact guide to the restoration needed. In order to support the visual presentation of 3D surface details, a hybrid approach combining data from laser scanning and digital imagery was developed. Studies of stone texture and spatial distribution of soluble salts were carried out at the monument in order to explain the mechanism of the weathering problem. Relative humidity, temperature, and wind are the main factors in the salt damage process. In order to study the effect of these conditions in the salt crystallization process a series of fi eldwork
1253D DIGITAL DOCUMENTATION IN PETRA
investigations and laboratory work were undertaken. The results show that visible zoning of weathering damage is correlated to different salt concentrations.
keywords damage assessment, 2D weathering form, 3D modelling, laser scanning, photogrammetry, salt content
Introduction
In 2007 the ancient city of Petra, the capital of the Nabataean empire from 400 bc
to ad 106, was selected to represent one of the ‘New Seven Wonders of the World’.
Petra’s temples, tombs, theatres, and other buildings, which are carved into rose-
coloured sandstone cliffs are scattered over 400 square miles. In 1985 Petra was
inscribed into the UNESCO list of world cultural heritage. However, the majority of
its monuments have deteriorated at a fast pace over recent years (Bumbaru et al.,
2000: 123). Due to this fact, in 1998 the World Monument Fund inscribed Petra into
the list of the one hundred most endangered monument assemblies in the world. The
city, located in south-western Jordan, suffers from weathering and erosion problems.
Problems result from the mainly porous inorganic materials of the monuments and
the uncontrolled environmental conditions around them. This weathering results in
potential salt damage as the main force on the monument’s stone structure (Fitzner
& Heinrichs, 2001: 12; Goudie & Viles, 1997; Eklund, 2008).
Reliable monitoring on weathering did not exist for most of the monuments in
ancient Petra. This is due to the lack of referential archive documents on the state of
weathering damage in the past (Heinrichs, 2008: 643; Kühlenthal & Fisher, 2000).
Recently, a large number of digital investigation methods have been newly developed
for reliable, easy, and fast surveying of large-scale monuments, including those that
are diffi cult to access. The integration of these techniques with the laboratory analy-
sis allows for a quantitative registration, documentation, and evaluation of complete
monuments.
This study aims to present a combined documentation and evaluation approach
that can be applied, in order to provide reliable information on the measurement and
characteristics of the stone decay problem at Al-Deir monument in Petra. The work
included a correlation study between the environmental conditions and surface wea-
thering using 2D mapping of the weathering forms and 3D realistic modelling of both
the geometry and radiometric properties of the surface details. The data could be used
in future studies of conservation action at the site.
The fi rst part of this paper presents a literature review for the main environmental
conditions that affect the architecture of Petra. The second part discusses the different
mapping methods used in the in situ surveying, including 2D mapping of the weath-
ering forms and digital photogrammetric techniques. Section 3 presents the weather-
ing mapping forms for Al-Deir. The methodology for the generation of accurate
and realistic 3D models of the Al-Deir monument, combining photogrammetry and
laser scanning, is presented in section 4. The environmental monitoring data and
chemical analysis of the salt content of the samples collected from the monument are
presented in section 5. In section 6 the results are discussed and concluded.
126 YAHYA ALSHAWABKEH et al.
Literature review
Petra: weathering agentsNatural processes and human activities, as well as a lack of maintenance in the
ancient city of Petra, are all involved in the weathering processes. Petra is located in
a tectonically active region: Barjous and Jaser (1992) traced three major faults in the
area. Due to the high seismic slip between these faults, the area has suffered from a
series of serious destructive earthquakes since ancient times. Most of the Theatre
was destroyed in ad 363, and another earthquake in ad 747 destroyed most of the
monuments in the centre of the city. Generally, statistics showed that an earthquake
with a magnitude above 6 on the Richter scale occurs every hundred years in the
Petra area (UNESCO, 1992).
The annual rainfall in Petra is very low, but it falls in a very short period of time.
Water erosion is, therefore, a very active agent in this environment. The Nabatean
hydrological systems show that the Nabateans were very aware of water erosion as
a problem in their area; they constructed ceramic pipes along the bedrock and the
face of the monuments to protect them from fl ood water. Moreover, horizontal sur-
faces were covered with multiple mortar layers to minimize the effect of running
water on these features (Shaer & Aslan, 2000: 89). Unfortunately, nowadays, the
Nabatean water system is the main cause of water erosion at the site. Joints and
cracks that were created by earthquakes, as well as the clogging of the Nabatean
water channels, allow the Petra monuments to be eroded from within and without.
In brief, the monuments of Petra had been affected by groundwater, running water,
and rainwater through different mechanisms.
The American Centre of Oriental Research in Amman (ACOR, 1999) reported that
the water table in Petra is actually much higher at the dawn of the twenty-fi rst
century than it was at the dawn of the last millennium. The rising of the water table
in the area has had a major impact on many other deterioration mechanisms such as
salt crystallization and the dissolution or leaching of materials (clay minerals, for
example, since most of the Petra monuments were carved from sandstone with a high
clay content). In short, water is a major factor in the deterioration process in the city
of Petra through fl ood damage, rainwater, runoff water, and capillary action and
their subsequent effects such as salt damage. Wind is another important weathering
agent for the Petra monuments. Not only does it cause the destruction of monuments
due to wind-blown sand (UNESCO, 1992), but it also enhances the effects of other
weathering agents, such as salt crystallization. The effect of the wind-blown sand is
mainly restricted to the lower parts of the monuments (1–2 m height), as these parts
come into contact with sand particles (UNESCO, 1992).
Salt crystallization is another, if not the major, weathering agent for the Petra
monuments (Eklund, 2008). Previous studies, such as Al Naddaf’s (2002), showed that
drilled samples from the Petra monuments are rich in sodium chloride and calcium
sulphate, while the scraped samples from the monuments’ surfaces were dominated
by calcium sulphate.
Due to wide variations in temperature, both daily and seasonally, the monuments
in Petra suffer from what is known as ‘thermal shock’. This kind of weathering is
related to the fact that some minerals expand more than others at high temperatures
1273D DIGITAL DOCUMENTATION IN PETRA
and contract at low temperatures. A study of the temperature variations within a
24-hour cycle in Petra carried out by Fitzner & Heinrichs (1991: 908) showed a
difference of 20ºC in the stone temperature and a difference of 21.1ºC in the air
temperature. In another study of the effect of thermal shock, Paradise (1999: 353)
concluded that, as a weathering agent, thermal shock was more destructive in calcite-
cemented sandstones due to the fact that calcite expands 25x10−6 µm/°C m3 calcite
parallel to the C-axis and contracts 4.9x10−6 µm/°C normal to the same axis in
temperatures between 18–50°C. The current paper does not discuss the thermal shock
decay mechanism; however, it does present a detailed petrography of the case study
monument, the Al-Deir tomb (below).
Weathering form mapping and 3D modelling using photogrammetric
techniques
Precise classifi cation and mapping of the damage phenomena are required for charac-
terization, interpretation, and monitoring of the rate and types of weathering damage,
which affects the stone monuments at Petra. Mapping of the weathering forms allows
for a visual inspection of the surface damage, which is necessary for the recording of
the type, intensity, and distribution of the weathering factors at the stone monuments
(Fitzner et al., 2002: 315; Gillhuber et al., 2009; Siedel, 2008). Although the 2D map-
ping of weathering forms give us an idea about the distributions of the weathering
processes, condition assessment of the structure using an accurate 3D modelling of
the weathering damage is an important component of the remedial programme.
The 3D modelling of the monuments by complete surveying and assessment is real-
ized by the integration of 3D laser scanning and photogrammetry. By these means
spatial data, as well as detailed structural data, can be obtained. The availability of
a 3D realistic model easily allows multiple views and a virtual manipulation. The
purpose of such visual information may serve as a tool for the identifi cation of the
nature, extent and severity of the deterioration (Gaiani et al., 2001: 86; Fuentes et al.,
2007: 543). Mapping is required for characterization, interpretation, and monitoring
of the rate and types of weathering damage affecting the stone monuments at Petra.
The mapping of weathering forms presents a visual inspection of the surface damage,
which is necessary for recording the type, intensity, and distribution of the weathering
factors at the stone monuments. As an archive gathered over time, the 3D models
provide valuable information when restoration is required. In the case of damaged
monuments, the 3D digital model can provide reference data as an exact guide to the
restoration needed and with detailed high-resolution 2D images, the texturing of 3D
models can provide both stone texture and spatial distribution of weathering features
on the monument.
Different contact-free techniques have been used for generating realistic 3D models
of an object or building. Photogrammetry has a long history as a tool for effi cient and
accurate data acquisition, including cultural heritage applications (Grün et al., 2002:
363; El-Hakim et al., 2002: 58; Debevec, 1996). Photogrammetric measurement allows
3D data collection from multiple images (Figure 1). If a point is depicted in at least
two images at different viewpoints, its corresponding 3D object coordinates can be
determined.
128 YAHYA ALSHAWABKEH et al.
In order to determine 3D point coordinates from measurements in overlapping
images, information on the position and orientation of the camera at the time of
exposure are required. In addition to what is termed the exterior orientation, the
parameters of the interior orientation have to be provided: this describes the position
of the image plane with respect to the centre of projection of the camera. Both
exterior and interior orientations can be reconstructed if the object coordinates are
available for a number of the control points. For the orientation of multiple overlap-
ping images, tie points, i.e. corresponding image points are additionally used. If the
parameters of the exterior and interior orientations are available, the object and
image coordinates can be linked by the co-linearity equation. This equation mathe-
matically formulates the theory that a point in the object space, the projective centre
of the optics, and the corresponding point in image space, forms one straight line.
Applying this principle, the 3D coordinates of all points can be determined by a
spatial intersection of straight lines, if they are observed in at least two images. One
of the main advantages of photogrammetry is the potential to simultaneously record
both the geometry and the surface texture of the depicted objects. This is especially
important when attempting to generate 3D virtual models of historical monuments
or artefacts from archaeological excavations (Schindler et al., 2003: 463). On the
other hand, image-based modelling alone is diffi cult or even impractical for the parts
of surfaces where homogenous texture prevents the reliable measurement of point
correspondences. Additionally, the identifi cation, and manual or semi-automatic
measurement of points, can be very labour intensive, especially if dealing with a
complex structure that requires a considerable number of points to be captured.
Due to the disadvantages of close-range photogrammetry, laser scanning has
become a standard tool for 3D data collection for cultural heritage sites and historic
buildings (Boehler et al., 2001: 480). For 3D data collection almost all commercially
available terrestrial laser scanners apply the so-called time-of-fl ight measurement
principle. Within this approach distances to the respective object surface are derived
from run-time measurements of refl ected light pulses. Point clouds covering the visible
fi gure 1 Principle of photogrammetry for 3D object modelling.
1293D DIGITAL DOCUMENTATION IN PETRA
object surface can then be collected by scanning the respective area of interest. This
results in a very effective and dense measurement of surface geometry. This is espe-
cially useful for the 3D reconstruction of geometrically complex objects that are
typically encountered in cultural heritage applications. However, the achievable
accuracy of time for a fl ight scanner is relatively low and commonly results in
centimetre range. Another type of scanner is triangulation-based and consists of a
transmitting device, sending a laser beam at a defi ned, incrementally changed angle
from one end of a mechanical base. A CCD camera at the other end of the base
detects the returned laser spot. They have better accuracy in terms of measurements,
which depend on the triangle base relative to its height. Due to this it can only be
used for relatively small objects and short distances (Boehler et al., 2001), an example
is the Arius scanner.
In addition to geometric data collection produced by a laser scanner, texture
mapping is particularly important in the area of cultural heritage to help create more
complete documentation. Photo-realistic texturing can, for example, add information
about the structure’s condition, such as decay of the material, which is not present in
the 3D model. The interpretation of 3D point clouds from laser scanning can be
simplifi ed considerably, if high-resolution imagery from digital cameras is available
(Balis et al., 2004; Alshawabkeh et al., 2004: 424; Abdelhafi z, 2009). Some commercial
3D systems already provide model-registered colour texture by capturing the RGB
values of each LIDAR point using a camera already integrated in the system. These
images are frequently used for scan registration but are not suffi cient for high quality
texturing. High image quality is especially required to provide suffi cient visual qua lity
of 3D surface details such as decay forms and cracks as required for documentation.
The collection of such images presumes suitable lighting, which frequently require
camera stations that are different from the actual scanner position. Thus the use of
independent cameras that are aligned with a suitable mathematical approach is an
appropriate solution.
Mapping of weathering forms for the Al-Deir tomb (the monastery)
Al-Deir, meaning monastery in Arabic, received its name from the cave that is known
as the Hermit’s Cell. The journey to the Al-Deir Tomb, depicted in Figure 2, requires
climbing more than 2000 steps carved into the mountain. It is the largest and most
impressive façade in Petra. The façade is about 50 m wide and 45 m high (Khouri,
1986). It is divided into two storeys; the lower one has a simple doorway (8 m high)
with six columns topped by Nabatean capitals, the upper storey, which is better
preserved, has eight columns with a conical central roof crowned with an urn. The
main chamber in Al-Deir is huge (11.5 m by 10 m). A small part of it was used as a
meeting room (symposium), whereas the main part was a mausoleum for the king.
A huge area in front of the monument was levelled, and seems to have been used for
great congregations of people. There is no actual dating for Al-Deir, however, many
writers such as Bourbon (1999), Taylor (2001), and Khouri (1986) suggest the middle
of the fi rst century (ad 44–70). The monument’s location on the edge of a high
mountain and the presence of different levels of stone decay are the main reasons
for selecting this monument for sampling. The main weathering forms in Al-Deir
tomb are shown in Table 1, while the main weathering groups, weathering forms,
130 YAHYA ALSHAWABKEH et al.
and individual weathering forms at the Al-Deir Tomb, and their distribution across
the surface of the monument, are shown in Figure 3.
3D modelling using photogrammetry and laser scanning techniques
Sensors applied and 3D surface modellingA laser scanning system GS100, manufactured by Mensi S.A., France, was used to
collect 3D point data. It has a 360x60 degree fi eld of view. The maximum captured
range for this scanner is 100 m with a linear error of less than 6 mm. The system is
fi gure 2 Al-Deir Tomb, Petra, Jordan.
TABLE 1
THE MAIN WEATHERING GROUPS AND WEATHERING FORMS AT AL-DEIR TOMB
Main weathering group Main weathering forms
1. Loss of stone materials 1.1. Break out1.2. Back weathering 1.3. Relief1.4. Pitting1.5. Washout
2. Deposits on stones 2.1. Loose salt deposits (Efflorescence)2.2. Biological colonization (Colonization of high plants)
3. Detachments 3.1. Flaking 3.2. Scaling 3.3. Cantour scaling
4. Fractures 4.1. Faults4.2. Cracks
1313D DIGITAL DOCUMENTATION IN PETRA
able to capture 5000 points per second. During data collection a calibrated video
snapshot of 768x576 pixel resolution is additionally captured, which is automati-
cally mapped on to the corresponding point measurements. An example of the
coloured collected point clouds is presented in Figure 4. In addition to the laser data,
digital images were captured for photogrammetric processing using a calibrated
Nikon D2x camera, which provides a resolution of 4288x2848 pixels with a focal
length of 20 mm. These images were collected at almost the same time in order to
have the same lighting conditions, which results in similar radiometric properties as
needed for high quality colouring of the laser data. A single laser scan is usually not
suffi cient to cover a full structure. The number of scans necessary depends on the
shape of the object, the amount of self-occlusion and obstacles hindering the object’s
visibility from respective sensor stations, and the object size compared to the sensor
range. During the data collection at the Al-Deir tomb, scans from fi ve different
viewpoints were done to resolve the occlusions. The mountainous environment
surrounding Al-Deir restricted the choice of suitable viewpoint positions. In total, the
fi ve scans resulted in almost 3 million collected points.
All the 3D models have been processed using Innovmetric Software, PolyWorks,
and Mensi Real Work Survey Software. In general, the whole process for generating
the 3D model can be subdivided into three main steps: registration, meshing or trian-
gulation, and merging. For objects with a complex shape, a series of scans must be
undertaken. In this case each scan has its own local coordinate system. The recon-
struction of the 3D model of the surveyed object requires the registration of the scans
in a single local reference system. This phase can be performed in an interactive
fi gure 3 2D mapping of the main weathering forms of Al-Deir Tomb.
132 YAHYA ALSHAWABKEH et al.
fi gure 4 Al-Deir façade recorded by terrestrial laser scanning: a) Overview b) Detailed view of collected point cloud.
1333D DIGITAL DOCUMENTATION IN PETRA
environment through the identifi cation of the homologous points in adjacent and
overlapping scans. Once the corresponding points are collected (of which there must
be at least three), the spatial transformation between the scans’ six-parameter trans-
formation can be estimated and all the corresponding points can be transferred into
the coordinate system that has been selected as the reference system. Figure 5 shows
the registration of two different scans used to cover the complete geometry of the
Monastery. The main aim of the triangulation (meshing) process is to convert the
point-based data into a visually more intuitive representation. Once the points are
collected in a single coordinate system, a triangulation algorithm is used to connect
the points to the meshes which represent the respective patches of the object surface.
Finally, in areas of overlapping scans redundant point measurements are eliminated
to reduce the size of the model, for the purposes of visualization or for further
post-processing. Figure 6 shows the 3D meshed model of the Al-Deir tomb.
A combined approach for realistic colouring of the laser dataAlthough the 3D model produced by the laser scanner contains a large number of 3D
data, which represent the object’s surface, it can still be diffi cult to recognize and
localize the outlines of the surface features. This is illustrated by comparison of
Figures 2 and 6: surface features such as structural cracks and edge outlines which
are clearly visible in Figure 2 are not discernible in the corresponding 3D meshed
model shown in Figure 6, as they are beyond the resolution of the available laser data.
In order to support the visual quality of such details, a hybrid approach combining
data from the laser scanner and the digital imagery was developed. Images from a
calibrated camera, and the high quality of the registration process of both data sets,
are crucial factors for achieving a realistic-looking model. This requires accurate
fi gure 5 Registration of two different scans in one coordinate system.
134 YAHYA ALSHAWABKEH et al.
determination of the camera’s interior and exterior orientation parameters. For our
investigations, the camera calibration parameters were computed using Australis
software. These parameters were used to eliminate geometric image distortions.
Corresponding coordinates between image and laser scanner were then measured
using the Photomodeler software, which was also applied to calculate the camera
position and orientation in the coordinate system of the geometric model. After the
position and orientation parameters are computed for the sensor stations, the co-
linearity equations, shown below, are then applied to calculate the image coordinate
for each point of the laser scanner point cloud. The implementation was realized
on a standard PC with an Intel 4, 3GHz Processor, and 1GB RAM using the C++
language.
xc r X X r Y Y r Z Z
r X X r Ya
A A A
A
=- - -
- -
− ( ) + ( ) + ( ) ( ) +
11 0 12 0 13 0
31 0 32 0 YY r Z Z
yc r X X r Y Y r Z Z
A A
a
A A A
( ) + ( ) − ( ) + ( ) + ( )
33 0
21 0 22 0 23 0
-
=- - -
( ) + ( ) + ( ) r X X r Y Y r Z ZA A A31 0 32 0 33 0- - -
In these equations:
xa, ya: an object A’s image coordinates.
XA, YA, ZA: the object’s coordinates in object space.
Xo, Yo, Zo: the object space coordinates of the camera position.
r11–r33: the coeffi cients of the orthogonal transformation between the image
plane orientation and the object space orientation, and are functions of the
rotation angles.
c: camera focal length.
fi gure 6 3D meshed Model for Al-Deir Tomb.
1353D DIGITAL DOCUMENTATION IN PETRA
As it can be seen in Figure 7, the different acquisition time of the images collected
from the laser scanner camera results in considerable differences in brightness and
colour, which changes the appearance of the textured 3D model. By contrast, the
proposed method for mapping high resolution digital images onto the geometry gives
a highly realistic appearance to the model and offers a descriptive view of the scene
which can be used for measuring and monitoring purposes, as depicted in Figure 8.
The measured point density for describing the surface of the monument was 2 cm
at the object; this is due to the nature of the used laser scanner which features 6 mm
accuracy. An example of a 3D model of a representative area of damage is given in
Figures 9 and 10. As can be seen, the mapping of close and detailed high resolution
images to the 3D model allows a good visual inspection of the surface damage, which
is necessary for recording of the weathering factors at the stone monument according
to type, intensity and spatial distribution.
Environmental monitoring and salt analysis
The activation of salt damage is highly controlled by the surrounding environmental
conditions. Relative humidity, air temperature, solar radiation, wind direction,
and wind speed are known as important factors that directly infl uence the salt
damage process (Lubelli, 2006; Price, 2000; Steiger & Zeunert, 1996: 353; Price &
Brimblecombe, 1994: 90; Arnold & Zehnder, 1991: 103). Therefore, the collection of
climatic data from the case study site was an essential part of the current research.
The methodology for evaluating the role of environmental conditions on salt damage
behaviour in cultural and historical heritage sites varies signifi cantly. Some scholars,
fi gure 7 3D textured model of Al-Deir Tomb using images collected from the laser scanner camera (768x576 pixels).
136 YAHYA ALSHAWABKEH et al.
fi gure 8 3D textured model of Al-Deir Tomb using images of Nikon D2x camera (4288x2848 pixels).
fi gure 9 3D textured model (using close detailed high-resolution images).
fi gure 10 3D model corresponding to Figure 9.
1373D DIGITAL DOCUMENTATION IN PETRA
such as Tricio and Viloria (2002: 67) and Camuffo and Bernardi (1995: 7) have under-
taken a very detailed microclimate investigation in evaluating the effects of environ-
mental parameters on historic buildings, while others, such as Al Naddaf (2002),
prefer a basic monitoring programme to evaluate stone-weathering behaviour. A
series of fi eldwork investigations and laboratory work was undertaken in order to
study the effect of these parameters on the salt crystallization process. The detailed
monitoring approach was considered more appropriate for the current research
because it would provide a more systematic way of evaluating the salt damage
processes at different locations by comparing the microclimate data of each location
with its salt content. This included an eighteen-month programme of microclimate
monitoring for relative humidity, air temperature, and wind speed at the case study
location, accompanied by four sampling periods for the determination of the salt
content at the case study location. For the temperature and relative humidity
measurements, Gemini Tinytag Plus (TGP-1500) loggers were used, and were placed
near the gateway of the tomb. In addition, a Lutron hand anemometer (Am-4201)
was used to measure the wind speed at the case study monument.
Recorded environmental conditions The temperature readings were much more stable than the relative humidity readings
(Figure 11). For example, in January the temperature readings ranged between 9.6
fi gure 11 Diagram combining relative humidity and temperature readings from the data logger. Location: Al-Deir Tomb (Recorded period: September 2003–January 2004).
138 YAHYA ALSHAWABKEH et al.
and 25.1ºC with an average of 12.5ºC. The daily fl uctuation range was less than 2ºC
during this month. Even though the relative humidity overall monthly averages did
not differ greatly, the individual relative humidity readings varied signifi cantly. For
instance, during January the relative humidity reached its maximum (82.1%) and
dropped to 54% toward the end of the same month. May, June, July, September, and
October were moderately dry and hot, while November and December had similar
humidity averages but were colder. January and February were slightly humid and
quite cold months. In March and April both temperature and relative humidity were
unstable with overall humid and rather cold conditions.
Generally, the Petra microclimate data is typifi ed by the domination of dry, hot
conditions and fl uctuating wind speeds throughout the majority of the year. In addi-
tion, the high rate of fl uctuation of the relative humidity and wind speed around the
studied monuments was very obvious. A considerable variation was also noted
between readings that came from the same monument and at the same time, but from
different sampling points.
Petrography of the AL-Deir stoneThe Al-Deir Tomb is carved out of Upper Umm Ishrin sandstone, which is multicol-
oured sandstone from the subarkosic Umm Ishrin formation of the middle to late
Cambrian age. The thin section of this stone (depicted in Figure 12) shows multicol-
oured, fi ne to medium, sub-angular to sub-rounded grained sandstone. Iron oxides
and kaolinite are the main matrix. Quartz grains make up over 80% of the stone
content. Porosity is moderate, with total porosity around 15% and mainly medium
(1–10 µm) to coarse pores (10–100 µm radii).
Salt types and distributionsThe determination of the salt types and their distribution in the Al-Deir tomb
at Petra has great importance for understanding and evaluating the weathering
processes at the monument. The types of salts, their depth of accumulation, the pore
structure and moisture regimes, as well as the surrounding microclimate conditions,
are key features controlling the decay of stone materials (Nicholson, 2001: 819;
Rodriguez-Navarro et al., 1999: 1250; Winkler, 1994; Doehne, 1994: 143; Rossi-
Manaresi & Tucci, 1991: 53).
fi gure 12 Photomicrograph of the petrological thin section of the Upper Umm Ishrin sandstone specimen. Field of view 2.5 mm. Magnifi cation: 40x(ppl).
1393D DIGITAL DOCUMENTATION IN PETRA
The Al-Deir Tomb is located on the edge of a high mountain and it has two
different levels of stone decay between its two storeys. The lower part of the Al-Dier
monument, as seen in Figure 8, had a wide range of stone decay features that are
mainly linked to salt damage, such as scaling. The latter feature was the main reason
for evaluating the salt distribution in order to match the weathering form on this
monument and the salt distribution.
Sampling profi les Two sampling profi les were taken from the Al-Deir Tomb, D1 and D2, as depicted
in Figure 13; to minimize the level of intervention neither was from the carved façade.
These two profi les were selected after a geological correlation with the tomb rocks,
and the heights of the profi les where chosen at levels where a high salt content
was expected due to the stone decay features at the tomb. Thirty-two samples were
collected from this area during the fi rst fi eldwork visit using a manual drill. At profi le
D1, samples were collected from three different depths (0–1, 1–3, and 3–5 cm), whilst
at D2 samples were collected from only two different depths (0–1 and 1–3 cm). The
current study applied sampling techniques that could not get further into the rocks
due to their hardness, especially in profi le D2. For the rest of the fi eldwork visits,
between 22–26 samples were collected and the sampling depths were reduced to two
intervals only (0–1 and 1–3 cm), due to the low content of the salt damage at the
3–5 cm interval.
Cation and anion content analysisIn order to identify the total salt content in each of the samples collected from each
monument at the four sampling fi eldwork visits, the cation and anion content of these
fi gure 13 The sampling profi les at Al-Deir Tomb D1 and D2.
140 YAHYA ALSHAWABKEH et al.
samples was measured. Before carrying out the analysis, the samples were diluted
with distilled water. A sample of 0.2P0.0005 g was diluted with 10P0.05 ml of
distilled water. The samples were fi ltered in order to avoid any metal debris from the
drills affecting the results. The cation analysis was carried out using an Inductively
Coupled Plasma Atomic Emission Spectrometer (ICP-AES). This machine was capa-
ble of measuring the following cations: calcium, sodium, iron, aluminium, magne-
sium, potassium, titanium, and zinc. The machine was calibrated automatically every
tenth sample. The anion content was measured using Ion Chromatography (IC). The
experiment was carried out with the same diluted samples that were used for the
ICP-AES in order to maintain homogeneous results. The samples were diluted further
when the anion concentration exceeded the capacity of the machine reading. The
cation content was measured using an Inductively Coupled Plasma Atomic Emission
Spectrometer (ICP-AES), while the anion content was measured using Ion chroma-
tography (IC). The total soluble content in all analyses was expressed as the weight
% of salt per weight unit of dried stone powder sample (0.2 g).
Results and discussionThe total soluble salts content at the Al-Deir Tomb was generally low (Table 2).
During the fi rst sampling season (August 2003), calcium and sodium were the main
cations, while sulphate, chloride, and nitrate were the main anions. Potassium and
phosphate were minor components. There was an obvious general trend of the total
content of soluble salts in the three sampling depth intervals. The salt content started
very low at 5 cm and increased gradually until it reached its maximum at 105 cm,
after which it started to decline again at 155 cm. Thereafter, the salt content increased
gradually with height. The signifi cant increase of the total soluble salt content at
105 cm is mainly related to the presence of a small terrace (40 cm widex250 cm long)
at the height of about 95 cm. This terrace could be the main source of water
accumulation and, therefore, an additional source of soluble salts. The increase of
the total soluble salt content was accompanied by a noticeable increase of bromide
content in the samples. The origin of the bromide is unknown. It should be noticed
here that these readings are from one fi eldwork session, and not for the whole
monitoring period.
During the winter season, sodium and calcium were the main cations, while potas-
sium and magnesium were present in low concentrations. Sulphate and chloride were
the main anions. A high concentration of nitrate was found in a few samples that
came mainly from the lowest level of the sampling profi le (5 cm height). During the
early summer fi eldwork visit (June 2004), the total soluble salt content at the Al-Deir
Tomb was slightly higher than in the previous two visits, with a more uniform
distribution of the salts throughout the profi le. Generally, the higher evaporation
rates during this period resulted in higher soluble salt content in the deeper intervals,
creating a more uniform distribution of the soluble salts between the surface and the
deeper intervals (0–1 and 1–3 cm).
The cation and anion analysis of the samples from the fi rst profi le (D1) at the
Al-Deir Tomb during the spring sampling fi eldwork visit showed the lowest overall
soluble salt content from all fi eldwork visits (Table 3). The excess of cation charges
compared to anion charges in these samples was one of the main features in these
1413D DIGITAL DOCUMENTATION IN PETRA
results. This excess was noticed in most of the samples from the previous fi eldwork
visits, but was higher in the samples from the spring and winter fi eldwork visits. The
winter and spring seasons were the most humid ones compared to the early and late
summer periods, causing higher groundwater levels inside the monuments. This situ-
ation strongly supports the authors’ arguments regarding the presence of carbonate
or bicarbonate anions in the samples from the Al-Deir Tomb that originated mainly
from groundwater inside the monument. However, despite the non-proportional
distribution of the cations and anions, a correspondence of calcium and sulphate and
of sodium and chloride ions existed throughout the profi le.
It is worth mentioning that the current research had tested the moisture content
in few samples from the Al-Deir area and the results showed a clear indication
that groundwater is the main source of moisture in the tested section. The evaluation
of salt distribution has shown that it is noticeably higher at the lower levels of
this monument compared to the higher ones. The groundwater may have a direct
infl uence on the salt distribution since it is the main source of these salts. Thus, the
TABLE 2
THE SOLUBLE SALT CONTENT FROM DRILLED SAMPLES, AL-DEIR TOMB, LOCATION (D1). FIRST FIELDWORK VISIT: AUGUST 2003
Sample number Location Height (cm) Depth (cm) Soluble salt content in the sample (%) of dry weight
79 D1 5 surface 0.25
80 D1 5 1 0.12
81 D1 5 1–3 0.13
82 D1 5 3–5 0.17
83 D1 55 0–1 0.22
84 D1 55 1–3 0.13
85 D1 55 3–5 0.11
86 D1 105 0–1 0.41
87 D1 105 1–3 0.24
88 D1 105 3–5 0.44
89 D1 155 Surface 0.36
90 D1 155 0–1 0.40
91 D1 155 1–3 0.15
92 D1 155 3–5 0.10
93 D1 205 Surface 0.21
94 D1 205 0–1 0.35
95 D1 205 1–3 0.09
96 D1 205 3–5 0.18
97 D1 255 0–1 0.44
98 D1 255 1–3 0.16
99 D1 255 3–5 0.19
142 YAHYA ALSHAWABKEH et al.
TABLE 3
THE MAIN ANION CONTENT OF DRILLED SAMPLES FROM AL-DEIR TOMB, LOCATION (D1) (DEPTH INTERVALS: 0–1 AND 1–3 CM). THIRD FIELDWORK VISIT: JUNE 2004
Location Height (cm)
Depth (cm)
Ca (ppm)
Na (ppm)
Mg (ppm)
K (ppm)
F (ppm)
Br (ppm)
Cl (ppm)
NO3 (ppm)
SO4 (ppm)
D1 5 0–1 15.90 24.40 1.90 0.00 2.24 0.00 22.81 7.27 22.70
D1 5 1–3 8.90 12.40 0.00 0.00 0.00 0.00 16.75 5.13 10.31
D1 55 0–1 20.30 18.50 0.00 0.00 2.21 0.00 16.29 5.79 19.50
D1 55 1–3 11.10 11.60 0.00 0.00 1.00 0.00 15.21 5.01 13.37
D1 105 0–1 12.70 9.20 1.50 0.00 4.44 0.00 10.12 10.98 21.01
D1 105 1–3 9.00 11.70 0.00 0.00 5.63 0.00 12.31 10.52 8.63
D1 155 0–1 11.30 13.00 0.00 0.00 1.85 0.00 12.28 11.32 12.47
D1 155 1–3 6.60 8.90 0.00 0.00 5.05 0.00 8.98 0.00 3.34
D1 205 0–1 21.60 17.90 1.80 0.00 1.87 0.00 17.91 11.48 57.37
D1 205 1–3 6.50 10.40 0.00 0.00 0.01 0.00 12.67 8.96 6.84
D1 255 0–1 13.60 10.50 0.00 0.00 0.01 0.00 11.83 10.94 21.14
D1 255 1–3 7.70 17.40 0.00 0.00 1.91 0.00 15.46 11.79 11.78
main decay line at this monument is directly linked to the salt damage problem, since
the highest salt accumulations were along this line.
Conclusions
Uncontrolled environmental conditions and salt content represent the main damage
processes for the Al-Deir monument in the ancient city of Petra in Jordan. This gave
rise to the need to have a comprehensive study and full documentation of the monu-
ment in order to evaluate its status. This research applied a comprehensive approach
utilizing 2D weathering form mapping and 3D modelling using laser scanning and
photogrammetry. 3D laser scanner technology was one of the important technical
methods used to acquire spatial data of the monument. The data collected can be
used to evaluate what restoration is required. In the case of damaged areas, the
detailed high-resolution 2D images and the texturing 3D models of the monument
will give both stone texture and spatial distribution of the weathering features and
will help to explain the mechanism and rate of the weathering problem.
The present study also included laboratory analysis and a correlation study of
the salt content and the surface weathering damage, which are the main damage
processes at work on the stone at the monument, allowing an understanding of the
deterioration mechanisms and causes. The evaluation of the salt distribution has
shown that the visible zoning of weathering damage correlates to different salt
concentrations.
Bibliography
Abdelhafi z, A. 2009. Integrating Digital Photogrammetry and Terrestrial Laser Scanning. Unpublished PhD thesis,
Institute for Geodesy and Photogrammetry, Technical University Braunschweig.
1433D DIGITAL DOCUMENTATION IN PETRA
Al Naddaf, M. 2002. Weathering Mechanisms: Technical Investigation in Relation to the Conservation of the
Sandstone Monuments in Petra, Jordan. Berlin: Mensch and Buch Verlag.
Alshawabkeh, Y. & Haala, N. 2004. Integration of Digital Photogrammetry and Laser Scanning for Heritage
Documentation. In: M. Orhan Altan, ed. Geo-Imagery Bridging Continents, Proceedings of the XXth ISPRS
Congress, 12–23 July 2004 Istanbul, Turkey. Commission V, pp. 424–29 [accessed 20 June 2010]. Available at:
<http://www.isprs.org/proceedings/XXXV/congress/comm5/papers/590.pdf>
American Centre of Oriental Research (ACOR) 1999. Petra, Jordan: Conservation in an Ancient City. Amman:
ACOR Publications, pp. 1–15 [accessed 3 December 2009]. Available at: <http://student.rwu.edu/users/ah1826/
ah1826/Petra/PPPETRA.htm>
Arnold, A. & Zehnder, K. 1991. Monitoring Wall Paintings Affected by Soluble Salts. In: S. Cather, ed. The
Conservation of Wall Paintings. Proceedings of a Symposium Organized by the Courtauld Institute of Art,
University of London, and the Getty Conservation Institute, London. July 13–16, 1987. Los Angeles: Getty
Conservation Institute, pp. 103–35.
Balis, V., Karamitsos, S., Kotsis, I., Liapakis, C. & Simpas, N. 2004. 3D Laser Scanning: Integration of Point
Cloud and CCD Camera Video Data for the Production of High Resolution and Precision RGB Textured
Models: Archaeological Monuments Surveying Application in Ancient Ilida. In: Proceedings of FIG Working
Week 2004, The Olympic Spirit in Surveying [accessed 20 June 201]. Available at: <https://www.fi g.net/pub/
athens/papers/wsa2/WSA2_5_Balis_et_al.pdf>
Barjous, M. O. & Jaser, D. 1992. Geotechnical Studies and Geological Mapping of Ancient Petra City. Amman:
The Hashemite Kingdom of Jordan, Ministry of Energy and Mineral Resources, Natural Resources Authority,
Geology Directorate, Geological Mapping Division.
Boehler, W., Heinz, G. & Marbs, A. 2001. The Potential of Non-Contact Close Range Laser Scanners for
Cultural Heritage Recording. In: J. Albertz, ed. Proceedings 18th International Symposium CIPA 2001 Potsdam
(Germany), September 18–21, 2001, pp. 430–36 [accessed 20 June 2010]. Available at: <http://cipa.icomos.
org/text%20fi les/potsdam/2001-11-wb01.pdf>
Bourbon, F. 1999. Petra: Art, History and Itineraries in the Nabateans Capital. Italy: White Star S.R.I. Publication,
pp. 1–15.
Bumbaru, D., Burke, S., Petzet, M., Truscott, M. & Ziesemer, J. 2000. Jordan — Heritage @ Risk! In: Heritage
at Risk, ICOMOS World Report 2000 on Monuments and Sites in Danger. Munich: ICOMOS, pp. 123–24.
Camuffo, D. & Bernardi, A. 1995. The Microclimate of Sistine Chapel. European Cultural Heritage Newsletter
on Research, 9: 7–32.
Debevec, E. 1996. Modelling and Rendering Architecture from Photographs. Unpublished PhD thesis, University
of California at Berkeley.
Doehne, E. 1994. In Situ Dynamic of Sodium Sulfate Hydration and Dehydration in Stone Pores: Observation of
High Magnifi cation Using the Environmental Scanning Electron Microscope. In: V. Fassina & F. Zezza, eds.
Third International Symposium on the Conservation of Monuments in the Mediterranean Base. Brescia: Grafo,
pp. 143–50.
El-Hakim, S., Beraldin, A. & Picard, M. 2002. Detailed 3D Reconstruction of Monuments Using Multiple
Techniques. In: W. Boehler, ed. Proceedings of the CIPA WG 6 International Workshop on Scanning for
Cultural Heritage Recording, Corfu, Greece, pp. 58–64. NCR 44915 [assessed 08 August 2010]. Available at:
<http://iitatlns2.iit.nrc.ca/iit-publicationts-iti/docs/NRC-44915.pdf>
Eklund, S. 2008. Stone Weathering in the Monastic Building Complex on Mountain of St Aaron in Petra, Jordan.
Unpublished Masters thesis, University of Helsinki, Department of Archaeology [accessed 08 August 2010].
Available at: <https://oa.doria.fi /bitstream/handle/10024/43682/stonewea.pdf?sequence=1>
Fitzner, B. & Heinrichs, K. 1991. Weathering Forms and Rock Characteristics of Historical Monuments Carved
from Bedrocks in Petra/Jordan. In: S. Baer, C. Sabbioni & A. Sors, eds. Science, Technology and European
Cultural Heritage. Proceeding of the European Symposium. Bologna, Italy: Butterworth-Heinemann Ltd,
pp. 908–11.
Fitzner, B. & Heinrichs, K. 2001. Damage Diagnosis at Stone Monuments — Weathering Forms, Damage Catego-
ries and Damage Indices. In: R. Prikryl & H. A. Viles, eds. Abstracts to the International Conference ‘Stone
weathering and atmospheric pollution network (SWAPNET)’, 7–11 May 2001, Prachov Rocks, Czech Republic.
Acta Universitatis Carolinae, Geologica, 45(1): 12–13.
144 YAHYA ALSHAWABKEH et al.
Fitzner, B., Heinrichs, K. & La Bouchardier, D. 2002. Damage Index for Stone Monuments. In: E. Galan & F.
Zezza, eds. Protection and Conservation of the Cultural Heritage of the Mediterranean Cities, Proceedings of
the 5th International Symposium on the Conservation. Lisse, Netherlands, pp. 315–26.
Fuentes, L. M., Finat, J., Fernández Martín, J. J., Martínez, J. & Sanjosé, J. I. 2007. Some Experiences in 3D
Laser Scanning for Assisting Restoration and Evaluating Damage in Cultural Heritage. In: J. Nimmrichter, W.
Kautek & M. Schreiner, eds. Lasers in the Conservation of Artworks, LACONA VI Proceedings, Vienna,
Austria, Sept. 21–25, 2005 (Springer Proceedings in Physics 116). London: Springer, pp. 543–53.
Gaiani, M., Gamberini, E. & Tonelli, G. 2001. VR as Work Tool for Architectural and Archaeological Restora-
tion: the Ancient Appian Way 3D Web Virtual GIS. In: H. Thwaites & L. Addison, eds. Proceedings of the 7th
International Conference on Virtual Systems and Multimedia, Berkeley, California, October 25–27. Berkeley,
California: IEEE Computer Society, pp. 86–95.
Gillhuber, S., Lehrberger, G. & Thuro, K. 2009. Teplá Trachyte Weathering Phenomena and Physical Properties
of a Volcanogenic Building Stone. In: M. Culshaw, H. Reeves, T. Spink & I. Jefferson, eds. IAEG Engineering
geology for tomorrow’s cities. Proceedings of the tenth International Congress IAEG, Nottingham, United
Kingdom. Bath: Geological Society Engineering Geology Special Publication. CR Rom — Paper Nr. 469, Theme
11.
Goudie, A. & Viles, H. 1997. Salt Weathering Hazards. Chichester: John Wiley & Sons Ltd.
Grün, A., Remondino, F. & Zhang, L. 2002. Reconstruction of the Great Buddha of Bamiyan, Afghanistan.
International Archives of Photogrammetry and Remote Sensing, 34(5): 363–68.
Heinrichs, K. 2008. Diagnosis of Weathering Damage on Rock-Cut Monuments in Petra, Jordan. Environmental
Geology, 56(3): 643–75.
Khouri, R. 1986. Petra: A Guide to the Capital of Nabateans. London: Longman Publication.
Kühlenthal, M. & Fisher, H. eds. 2000. Petra. Die Restaurierung der Grabfassaden [The Restoration of the
Rockcut Tomb Façades]. Munich: Arbeitshefte des Bayerischen Landesamtes für Denkmalpfl ege.
Lubelli, B. 2006. Sodium Chloride Damage to Porous Building Materials. Unpublished PhD thesis, Politecnico di
Milano, Italy.
Nicholson, D. 2001. Pore Properties as Indicators of Breakdown Mechanisms in Experimentally Weathered
Limestone. Earth Surface Processes and Landforms, 26: 819–38.
Paradise, T. 1999. Analysis of Sandstone Weathering of the Roman Theatre in Petra, Jordan. ADAJ (Annual of
the Department of Antiquities, Amman — Jordan), 43: 353–68.
Price, C. A. ed. 2000. An Expert Chemical Model for Determining the Environmental Conditions Needed to
Prevent Salt Damage in Porous Materials. European Commission Report 11, Protection and Conservation of
European Cultural Heritage. London: Archetype Publications.
Price, C. A. & Brimblecombe, P. 1994. Preventing Salt Damage in Porous Materials. In: A. Roy & P. Smith, eds.
Preventive Conservation, Practice, Theory and Research. London: International Institute for Conservation of
Historic and Artistic Works, pp. 90–93.
Rodriguez-Navarro, C., Doehne, E., & Sebastian, E. 1999. Origins of Honeycomb Weathering: The Role of Salts
and Wind. Geological Society of America Bulletin, 111(8): 1250–55.
Rossi-Manaresi, R. & Tucci, A. 1991. Pore Structure and the Disruptive or Cementing Effect of Salt Crystalliza-
tion in Various Types of Stone. Studies in Conservation, 36: 53–58.
Schindler, K., Grabner, M. & Leberl, F. 2003. Fast On-Site Reconstruction and Visualization of Archaeological
Finds. In: M. O. Altan, ed. Proceedings of the 19th International CIPA Symposium, Antalya, pp. 463–68.
Shaer, M. & Aslan, Z. 2000. Nabataean Building Techniques with Special Reference to the Architecture of Tomb
825. In: M. Kühlenthal & H. Fisher, eds. Petra: The Restoration of the Rockcut Tomb Façades. Munich:
Bayerisches Landesamt für Denkmalpfl eg, pp. 89–109.
Siedel, H. 2008. Salt-Induced Alveolar Weathering of Rhyolite Tuff on a Building: Causes and Processes.
In: Proceedings of the International Conference on Salt Weathering on Buildings and Stone Sculptures,
Copenhagen, 22–24 October, 2008. Copenhagen: The National Museum of Denmark.
Steiger, M. & Zeunert, A. 1996. Crystallization Properties of Salt Mixtures: Comparison of Experimental Results
and Model Calculation. In: J. Riederer, ed. Proceedings of the Eighth International Congress on the Deteriora-
tion and Conservation of Stone. Berlin, 30 September–4 October 1996. Berlin: Möller druck und verlag,
pp. 535–44.
Taylor, J. 2001. Petra and the Lost Kingdom of the Nabataeans. London: I. B. Tauris.
1453D DIGITAL DOCUMENTATION IN PETRA
Tricio, V. & Viloria, R. 2002. Microclimatic Study of a Historical Building. In: E. Galaán & F. Zezza, eds.
Protection and Conservation of the Cultural Heritage of the Mediterranean Cites. Lisse: Sweets and Zeitlinger,
pp. 67–70.
UNESCO, 1992. Petra National Park Management Plan. Unpublished report. Coordinators: B. Lane & B.
Bousquet.
Winkler, E. 1994. Stone in Architecture: Properties, Durability, 3rd ed. Berlin: Springer-Verlag Publications.
Notes on contributors
Yahya Alshawabkeh is Head of the Department of Conservation Science at the Queen
Rania Institute of Tourism & Heritage in Jordan.
Correspondence to: Yahya Alshawabkeh, The Hashemite University, PO Box
150459, Zarqa 13115, Jordan. Email: [email protected]
Fadi Bal’awi is Assistant Professor in Conservation Science in the Department of
Conservation Science at Queen Rania’s Institute of Tourism and Heritage.
Correspondence to: Fadi Bal’awi, The Hashemite University, PO Box 150459,
Zarqa 13115, Jordan. Email: [email protected]
Professor Norbert Haala is Deputy Director of the Institute for Photogrammetry, at
the University of Stuttgart.
Correspondence to: Norbert Haala, Institute for Photogrammetry, University of
Stuttgart, Geschwister-Scholl-Strasse 24D, D-70174 Stuttgart, Germany.
Copyright of Conservation & Management of Archaeological Sites is the property of Maney Publishing and its
content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for individual use.