Road building technology has connected our cities and villages and lays at the basis of modern infrastructure. But there was a time developed roads did not exist and most roads were solely made of brick stones or dirt.
Before 260 BC roads were not very common across the world, ancient roads were commonly made by cutting away trees, hardening them or placing brick stones to fortify them. The first roads must have started to appear when trade routes came into existence across ancient Sumeria, India and China. Also large armies needing to stretch large distances made roads necessary for improved mobility.
As empires started to grow the need for reliable, strong roads grew. By 260 BC the lack of good accessible roads became a major problem for the Roman Empire, that spread across almost entire mid, western and southern Europe. The Roman armies needed to cross huge distances and they needed to do so by foot. As the armies grew in manpower so grew the difficulty to move them. Walking across muddy roads with a 10.000 men strong army was able to cause major problems during times of rain, making some roads inaccessible and creating a danger for certain areas when needing to sent reinforcements.
Engineers were gathered by the Roman command and put to the task to solve the problem of weak roads. The engineers experimented to find out the causes of why the roads were in such bad shape and started testing possible fixes. The first thing the engineers discovered was that over time roads were trampled with depressions in the ground making them filled with pools of water that tore the quality of the roads. Pooled water made the old roads turn quickly to mud and disintegrate. So came to be the first Roman road building principle: roads needed to be on a higher level than the surroundings and needed to get proper drainage to make it possible for the water to flow away. This also meant that every road needed to have a solid foundation.
The next thing the engineers set out to do was find out ways to spread the weight of the massive carts that the Roman armies needed for supplies and materials. They experimented with different top level surfaces for road building that were able to spread the weight of heavy wheels.
By 250 BC Roman engineers had developed a road building manual that would not be equaled for over 2000 years. Roman roads were carefully built in four layers and surveyed by special road inspectors. The names of these road layers still describe what we refer to as a road today, pavimentum or pavement was a trench for the road, lined with edging stones and made of smooth rammed earth. Next they would create a layer called a rudus on top of the hard dirt surface, the rudus was made out of concrete mixed with broken stones and tile. Its job was to provide drainage and to spread weight evenly onto the ground below. Above the rudus was placed the nucleus layer, a layer of slag or lime, chalk or tile. The nucleus acted as a cushen needing to absorb most of the stress of marching feet and heavy carts. Finally the top layer was called the summum dorsum or fitted flagstones, that were laid into place on top of the other layers.
Roman engineers constructed 372 major roads all across the Roman Empire, including more than 53,000 miles of developed road way that stretched from North Africa to Scotland and from Spain to Greece. Massive groups of slaves from conquered lands were set to the task on building the Roman roads. The work was brutal.
After the Roman Empire collapsed the French started to built a developed systematic road system during the 1730′s under direction engineer Ipierre Tresaguet.
Sources: 100 Greatest Science Inventions of All Time, by Kendall F. Haven, published 2006