By Steve Abrams May 16, 2013 

Thousands of years before urban planning, motor vehicles, or even the

wheel, the first roads appeared on the landscape. Just as molecules

coalesced into cells and cells into more complex organisms, our first

roads were spontaneously formed by humans walking the same paths

over and over to get water and find food. As small groups of people

combined into villages, towns and cities, networks of walking paths

became more formal roads. Following the introduction of the wheel about

7,000 years ago, the larger, heavier loads that could be transported

showed the limitations of dirt paths that turned into muddy bogs when it

rained. The earliest stone paved roads have been traced to about 4,000

B.C. in the Indian subcontinent and Mesopotamia.

A Roman Road At Pompeii. The Raised Stones Were An Early Crosswalk That Kept Pedestrians Up And Out Of The StreetUIG Via Getty Images

To help support the movement of legions throughout their empire, the

Romans developed techniques to build durable roads using multiple

layers of materials atop of deep beds of crushed stone for water drainage.

Some of those roads remain in use more than 2,000 years later, and the

fundamental techniques form the basis of today’s roads.

Modern road-construction techniques can be traced to a process

developed by Scottish engineer John McAdam in the early 19th century.

McAdam topped multi-layer roadbeds with a soil and crushed stone

aggregate that was then packed down with heavy rollers to lock it all

together. Contemporary asphalt roads capable of supporting the vehicles

that emerged in the 20th century built upon McAdams’ methods by

adding tar as a binder.

The actual process of road building has changed dramatically over the

past century, going from large gangs of workers with picks and shovels to

enormous specialized machines. Rebuilding existing roads starts with

peeling up existing pavement, grinding it and dumping it straight into

trucks for reuse later as aggregate for new roads. After grading the

surface, pavers come in and lay down fresh, continuous sheets of asphalt

followed directly by the rollers.