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Roman siege engines
Roman siege engines were, for the most part, adapted
from Hellenistic siege technology. Relatively small ef-
forts were made to develop the technology; however, the
Romans brought an unrelentingly aggressive style to siege
warfare[1] that brought them repeated success. Up to the
1st century BC the Romans utilized siege weapons only
as required and relied for the most part on ladders, tow-
ers and rams to assault a fortified town. Ballistae were
also employed, but held no permanent place within a le-
gion’s roster, until later in the Republic, and were used
sparingly. Julius Caesar took great interest in the integra-tion of advanced siege engines, organizing their use for
optimal battlefield efficiency.[2]
1 Army engineering corps
Roman springald .
Main article: Roman military engineering
To facilitate this organization and the army’s self-
sufficiency, an engineering corps was developed. An of-
ficer of engineers, or praefectus fabrum, is referenced in
armies of the Late Republic, but this post is not verifi-
able in all accounts and may have simply been a military
advisor on the personal staff of a commanding officer.[2]
There were legion architects (whose rank is yet unknown)
who were responsible for the construction of war ma-
chines who would also assure that all artillery construc-
tions in the field were level. Ensuring that construc-
tions were level was the job of the libratores , who would
also launch missiles and other projectiles (on occasion)
during battle (Le Bohec 1994: 52). The engineering
corps was in charge of massive production, frequentlyprefabricating artillery and siege equipment to facilitate
its transportation.[1]
2 Artillery
Roman siege engines
Roman artillery was very efficient at that time, and dur-
ing a siege the Romans would attack the weakest area of
their enemy’s defenses and attempt to breach the walls at
that point. To support this effort, artillery fire would com-
mence, with three main objectives:[3] to cause damage to
defenses, casualties among the opposing army, and loss ofenemy morale. It would also provide cover fire for troops
building siege ramps or those in siege towers. There
were machines called tormenta , which would launch
(sometimes incendiary) projectiles such as javelins, ar-
rows, rocks, or beams. These devices were on wheeled
platforms to follow the line’s advance. All were “predi-
cated on a principle of physics: a lever was inserted into
a skein of twisted horsehair to increase torsion, and when
the arm was released, a considerable amount of energy
was thus freed”.[3] It was later stated that sinew, instead
of twisted hair, provideda better “spring.” Theseweapons
were high-maintenance devices and vulnerable to having
their leather, sinew, or hemp skeins affected by wet oreven damp, which would cause them to slacken and lose
tension, rendering the engine useless.[4]
It is somewhat difficult to clearly define and describe Ro-
man artillery, as names are easily confused and historians
still do not agree on all definitions. Perhaps best known
are the ballista, the onager , and the scorpio.
2.1 Ballista
Main article: Ballista
After the absorption of the Ancient Greek City statesinto the Roman Republic in 146 BC, some advanced
Greek technology began to spread across many areas of
1
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2 2 ARTILLERY
Roman arrow machine.
One talent ballista (26 kg weight projectile). The heaviest versions
could shoot up to three talents (78 kg), possibly much more.[5]
A ballista.
Roman influence. This included the hugely advantageous
military advances the Greeks had made (most notably by
Dionysus of Syracuse), as well as all the scientific, math-
ematical, political and artistic developments.
The Romans 'inherited' the torsion powered Ballistae
which had by now spread to several cities around the
Mediterranean, all of which became Roman spoils of war
in time, including one from Pergamum, which was de-picted among a pile of 'trophy' weapons in relief on a
balustrade.
The torsion ballista, developed by Alexander, was a far
more complicated weapon than its predecessor, and the
Romans developed it even further.
Vitruvius, in his De Architectura Book X, describes the
construction and tuning of Ballistae.
Every century (group of 60-100 men) in the Roman army
had a ballista by the 1st century AD.[6] It was the com-
mand of the chief of the ballista, under whom were the
artillery experts, or doctores ballistarum and finally, the
artillerymen, or ballistarii .[7] Ballistae were heavy missile
weapons, hurling large rocks great distances to damage
rampart walls. They resembled large crossbows, rather
than catapults. They were powered by two horizontal like
arms, which were inserted into two vertical and tightly
wound “skein” springs contained in a rectangular frame
structure making up the head or principal part of the
weapon. The arms were drawn rearward with a winch
lever to further twist the skeins and thus gain the tor-
sion power to cast a projectile.[4] It has been said that the
whirring sound of a ballista-fired stone struck fear and
dread into the hearts of those inside the walls of besieged
cities. The stones chosen to be used in the ballista had tobe a particular sort. According to Vegetius river stones
were best, since they are round, smooth, and dense. Bal-
lista stones found at the site of Masada were chiseled to
make them as round as possible.[8]
2.1.1 Early Roman ballista
Roman 'catapult-nest' on Trajan’s Column
The early Roman ballistae were made of wood, and held
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2.2 The Onager 3
Ballista, military equipment of ancient Rome.
together with iron plates around the frames and iron nails
in the stand. The main stand had a slider on the top, into
which were loaded the bolts or stone 'shot'. Attached to
this, at the back, was a pair of winches and a claw, used
to ratchet the bowstring back to the armed firing position.
A slider passed through the field frames of the weapon,
in which were located the torsion springs (rope made of
animal sinew), which were twisted around the bow arms,
which in turn were attached to the bowstring.
Drawing the bowstring back with the winches twisted the
already taut springs, storing the energy to fire the projec-
tiles.
Theballista was a highly accurate weapon (there are many
accounts right from its early history of single soldiers be-
ing picked off by the operators), but some design aspects
meant it could compromise its accuracy for range. The
lightweight bolts could not gain the high momentum of
the stones over the same distance as those thrown by the
later onagers, trebuchets, or mangonels; these could be as
heavy as 90-135 kg (200-300 pounds).
The Romans continued the development of the Ballista,
and it became a highly prized and valued weapon in the
army of the Roman Empire.
It was used, just before the start of the Empire, by
Julius Caesar during his conquest of Gaul and on both
of his expeditions to Britain. Both attempted invasions
of Britain and the siege of Alesia are recorded in his own
Commentarii (journal), The Gallic Wars (De Bello Gal-
lico). It was also used in the Roman siege of Masada.
2.1.2 First invasion of Britain
The first invasion of Britain took place in 55 BC, after
a rapid and successful initial conquest of Gaul, in partas an exploratory expedition, and more practically to try
and put an end to the re-enforcements sent by the native
Britons to fight the Romans in Gaul.
A total of eighty transports, carrying two legions at-
tempted to land on the British shore, only to be driven
back by the many British warriors assembled along the
shoreline. The ships had to unload their troops on the
beach, as it was the only one suitable for many kilometers,yet the massed ranks of British charioteers and javeliners
were making it impossible.
Seeing this, Caesar ordered the warships –
which were swifter and easier to handle than
the transports, and likely to impress the na-
tives more by their unfamiliar appearance – to
be removed a short distance from the others,
and then be rowed hard and run ashore on the
enemy’s right flank, from which position the
slings, bows and artillery could be used by men
on deck to drive them back. This manoeuvre
was highly successful.
Scared by the strange shape of the warships,
the motion of the oars, and the unfamiliar ma-
chines, the natives halted and then retreated a
little. (Caesar, The Conquest of Gaul , p. 99)
2.1.3 Siege of Alesia
In Gaul, the stronghold of Alesia was under a Roman
siege in 52 BC, and surrounded by Roman fortifications.
As was standard siege technique at the time, ballistae
were placed up in the towers with other soldiers armedwith either bows or slings.
2.2 The Onager
Main article: Onager (siege weapon)
The onager was a post-classical Roman siege engine,
Sketch of an Onager, from Antique technology by Diels
which derived its name from the kicking action of the
machine, similar to that of an onager (wild ass). It isa type of catapult that uses torsional pressure, generally
from twisted rope, to store energy for the shot.
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4 3 BREAKING THE WALLS
The onager consisted of a frame placed on the ground
to whose front end a vertical frame of solid timber was
rigidly fixed; through the vertical frame ran an axle, which
had a single stout spoke. On the extremity of the spoke
was a sling used to launch a projectile.
In action the spoke was forced down, against the tensionof twisted ropes or other springs, by a windlass, and then
suddenly released. The spoke thus kicked the crosspiece
of the vertical frame, and the projectile at its extreme end
was shot forward.
The onagers of the Roman Empire were mainly used
for besieging forts or settlements. They would often be
loaded with large stones or rocks that could be covered
with a flammable substance and set alight.
In the Middle Ages (recorded from around 1200 C.E.)
a less powerful version of the onager was used that em-
ployed a fixed bowl rather than a sling, so that many small
projectiles could be thrown, as opposed to a single largeone. This engine was sometimes called the mangonel , al-
though the same name may have been used for a variety
of siege engines.
2.3 Scorpios
Main article: Scorpio (dart-thrower)
The scorpio was a crossbow-like device that fired smaller
Modern reconstruction of a Scorpio
arrows with deadly accuracy[2] used both in the field
and in sieges. They were so-named for their deadly,
armor-piercing sting and could be operated by just one
or two men. Scorpios were meant to kill and injure en-
emy troops, rather than break down enemy fortifications.
Thanks to their smaller size, they could be mounted on or
in siege towers. During the Siege of Amida, a scorpion-
fired arrow killed theson of Grumbate, king of the Chion-
itae, when he was approaching the city to surrender.[9]
There has been some research done into the exis-
tence of the self-loading, serial-fire scorpio or polybolos.Legionaries either side would continuously keep turning
cranks which turned a chain, which operated the various
mechanisms to load and fire the catapult. All that was
needed was for another soldier to keep feeding in more
arrows.[10]
3 Breaking the walls
3.1 Battering rams
Main article: Battering ram
Roman battering rams, or aries , were an effective
Roman battering ram.
A battering ram (aries) with a shed (testudo). After a relief on
Septimius Severus ' triumphal arc in Rome.
weapon for breaking down an enemy’s walls, as well as
their morale. Under Roman law, any defenders who
failed to surrender before the first ram touched their wall
were denied any rights.[11] The moment they heard the
ram hit the wall, those inside the city knew that the siege
proper had begun and there was no turning back.[12]
Josephus describes the battering ram used at Jotapata
thus:[13]
It is an immense beam, similar to a ship’s
mast, with one end covered with iron shaped
into a ram’s head; hence its name. It is sus-
pended from another beam like a balance arm
by cables around its middle, and this in turn
is supported at both ends by posts fixed in the
ground. It is drawn back by a huge number of
men who then push it forward in unison with all
their might so that it hits the wall with its ironhead. There is no tower strong enough nor any
wall thick enough to withstand repeated blows
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3.3 Mines 5
The remains of the Roman siege-ramp at Masada
of this kind, and many cannot resist the first
shock.
Vitruvius in De Architectura Book X describes the con-
struction and use of battering rams.
For protection, a battering ram was suspended in a mo-
bile shelter called a tortoise, or testudo. According to
Vegetius, it was given this name because the ram would
swing out of the shelter much like a tortoise’s head comes
out of its shell. Such shelters would provide the men
within protection against missiles and incendiary devices.
They were constructed from a framework of strong tim-
bers with planks and wicker hurdles on the sides. The en-
tire shelter would then be covered with a fireproof mate-rial such as uncured hides.[14] According to Apollodorus
of Damascus, the shelter should be fixed to the ground
while the ram was being used to both prevent skidding
and strain on the axles from the weight of the moving
apparatus. This would also increase the strength of the
impact on the walls.[15]
3.2 Siege towers
Main article: Siege towers
According to Josephus, the Roman siege towers at
Jotapata were 50 feet high and iron-plated to protect them
from fire; those at Masada were reported to be 75 feet
high. It was possible to have many different devices on
siege towers, such as artillery, draw bridges and rams.
Those at the top of the tower were to keep defenders off
the walls while those below them attempted to breach the
wall using ramps. In the battle of Jerusalem in 70 AD the
Romans began assault on the third defensive wall within
Jerusalem, the tower stood 75ft tall and was compromised
when the Jewish resistance tunneled underneath the tower
leading it to collapse. [16] Following a basic design, details
of tower construction varied from siege to siege and thereis no known treatise which specifies at which level siege
equipment should be placed. Vegetius noted that, “be-
Siege Machine.
siegers sometimes built a tower with another turret inside
it that could suddenly be raised by ropes and pulleys to
over-top the wall”.[17]
3.3 Mines
Mines could be dug under city walls as a means of en-
tering a city secretly and capturing it but were more fre-quently constructed to weaken city walls. Once dug,
sappers would underpin the walls with wood and cause
the walls to collapse by firing the supports with resin, sul-
fur and other incendiary materials.[18]
4 See also
• Roman engineering
• Vitruvius
5 Notes
[1] Goldsworthy 2000: 144
[2] Keppie 1984: 99
[3] Le Bohec 1994: 138
[4] Catapulta at LegionXXIV
[5] Werner Soedel, Vernard Foley: “Ancient Catapults”,
Scientific American, Vol. 240, No. 3 (March 1979),
p.120-128 (121ff.)
[6] Le Bohec 1994: p. 138
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6 6 REFERENCES
[7] Le Bohec 1994: p. 49
[8] Garrison 1997.
[9] Goldsworthy 2000: 191
[10] Siege weapons at roman-empire.net
[11] Goldsworthy 2000: p. 145
[12] Gilliver 1999: p. 140
[13] Le Bohec 1994: p. 139
[14] Gilliver 1999: pp. 134-135
[15] Gilliver 1999: p. 138
[16] Gilliver 1999: pp. 136-137.
[17] Gilliver 1999: 138
[18] Gilliver 1999: 140
6 References
• James V. Garrison (1997). “Casting stones: ballista,
stones as weapons, and death by stoning”. Brigham
Young University Studies 36 (3): 351–352.
• Gilliver, C.M. (1999). The Roman Art of War .
Charleston, SC: Tempus. ISBN 0-7524-1939-0.
• Goldsworthy, Adrian (2000). Roman Warfare.
London: Cassell. ISBN 0-304-35265-9.
• Keppie, Lawrence (1984). The Making of the Ro-
man Army from Empire to Republic . Totowa, NJ:
Barnes & Noble Books. ISBN 0-389-20447-1.
• Le Bohec, Yann (1994). The Imperial Roman Army.
London: B.T. Batsford Ltd. ISBN 0-7134-7166-2.
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7
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