What is a good description of an ancient Roman consular road?

Answer 1

Many historians who have written about ancient Roman roads give us a description of what many of these historians call consular roads. Clearly because the time of the early Roman Republic to the end of the western empire in 476 AD CE, road construction differed among the engineers who built them. Some roads were sophisticated ones that were unmatched in Europe until the 18th century. Other Roman roads that connected small towns & cities were not as refined as the main roads that connected major Roman cities with each other.
Most roads had a degree of commonality among them. The best roads had a pattern of construction that were "ahead of their time". The type of Roman road referred to as "consular" had these features. This is not to say that other roads did not share some of the same characteristics.
A consular road were true achievements in Roman engineering. Consular roads were anywhere between 16 to 24 feet in width.
As the roads approached Rome, part of the width was used for sidewalks. It seems that even having "sidewalks" is something to marvel. These sidewalks were paved with rectangular slabs of granite.
The basic consular road had these features:

A. As the shortest distance between two points is a straight line, and taking into consideration the practicality of Roman thought, features of nature that would interfere with a straight line were, at an extra price in time & effort, overcome. Streams & marshes were simply crossed with costly bridges. With the use of arched viaducts made from bricks & stones, the roads overcame steep hills & mountains were conquered by creeping along mountainsides & embankments secured with high retaining walls or tunneled through them.
Pavement varied with local materials provided they met Roman standards.
The bottom or first layer beneath the road was usually 4 to 6 inches of sand.
Sometimes an inch of mortar was used. Laid on top of this substructure were 4 layers of masonry. Then 12 inches of cement or clay was laid on top of the masonry. This was followed by 10 to 12 inches of rammed concrete.
As we near the surface of the road, stones of silex or lava polygonal slabs one to three feet in diameter.
Finally the upper surface were slabs of stone smoothed to the point and fit together as if it was all one piece.
The drainage was done by having the middle of the road beveled so that at the high point water rolled down to the "curbs" keeping the road passable.