Roman Engineering - Roads

Roads

Roman roads were constructed to be immune to floods and other environmental hazards. Many roads built by the Romans are still in use today.

There were several variations on a standard Roman road. Most of the higher quality roads were composed of five layers. The bottom layer, called pavimentum, was one inch thick and made of mortar. Above this were four strata of masonry. The layer directly above the pavimentum was called the statumen. It was one foot thick, and was made of stones bound together by cement or clay.

Above that, there were the rudens, which were made of ten inches of rammed concrete. The next layer, the nucleus, was made of twelve to eighteen inches of successively laid and rolled layers of concrete. Summa crusta of silex or lava polygonal slabs, one to three feet in diameter and eight to twelve inches thick, were laid on top of the rudens. The final upper surface was made of concrete or well smoothed and fitted flint.

Generally, when a road encountered an obstacle, the Romans preferred to engineer a solution to the obstacle rather than redirecting the road around it. Bridges were constructed over all sizes of waterway, marshy ground called for the construction of raised causeways with firm foundations, and hills and outcroppings were frequently cut or tunneled through rather than avoided. The tunnels were made with square hard rock block.