by Earl King

Created on: July 22, 2008

Ancient Roman road construction lessons
For modern engineers

Can it be possible that ancient Roman engineers were ahead of their modern day counterparts in some areas? I've read recently that we have not been giving ancient societies enough credit for their technology development. Let's explore the idea expressed in our title. To discover what the Romans did in their road construction let me recommend "The Ancient Engineers" by L. Sprague De Camp, 1960. The 1993 Barns & Noble edition that I have is in stores now.

What was the primary reason the Romans would have for building roads over 2000 years ago? I'm sure it was to get their army to the battle zone quickly. The army was mostly marching troops. Sometimes there was heavy infantry, siege towers and other engines of war.

The local civilian population provided a secondary reason. Wear and tear on these roads by peasants and their horse drawn carts was minor. Except for roads near the center of Roman control it seems to me that their impact upon the paved roads would also have been slight.

Roman roads were laid out as straight as the land and the environs would allow. They went over a hill instead of around it or cut through it. This sometimes left some very steep grades. As much as possible the road would be put on an embankment to keep travel surfaces above the level of the surrounding land. That helped to keep it clean and let the solders keep an eye out for the enemy.

The main paved roads were massive. Starting with a trench several feet deep, they would search for bedrock or at least soil which had a high bearing strength. If it proved to be too soft, they would resort to driving piles. These were basically poles made from trees driven vertically. Structures called piers may have been installed on top of the piles to transfer the load from the road to the foundation.

The road was built up in layers using local material when available. As an example, a fully paved road would have 4 or 5 layers. Altogether the layers were about 4 feet thick and 6 ft to 20 ft wide. The bottom was a layer of sand, mortar or both. Cement or lime mixed with sand and water made a good binder. And yes, they had a form of cement back then.

Next was a layer of flat, squared stones set in cement. Then came a layer of gravel set in clay or concrete. A layer of rolled sand concrete would follow. Finally a crowned pavement that was higher in the middle than the sides. It was of large, many sided blocks or hard rock set in concrete with

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