The Romans used science to some extent in building their roads. At the zenith of their power they had constructed about 85,000 kilometers of them. These roads connected the capital Rome with the boundaries of the vast empire. Rome was like a hub with 29 military roads going out in all directions. The most famous was the via Appia. Most archeologists think that the Romans learned the ability to construct roads particularly from the Etruscans in the North of Italy. Though also other cultures like the Phoenician and Egyptian ones must have contributed historically.
It is very noteworthy that Roman roads were made in straight lines from point to point. Lakes, swamps, ravines and even mountains were subdued. Even modern engineers admire them because of their courageous design.
The via Appia was started in 312 B.C. and consisted of one and one half meters of different materials. The deepest layer was made of sand or a kind of lime. On top of that they spread one half meter of flat stones. Then about 20 centimeters of smaller stones mixed with mortar. Then about 30 centimeters of pebbles and coarse sand mixed with hot lime. The top layer consisted of 15 centimeters of lava that looked like flints. People would imitate this practice the next 2000 years!
Roman public transport was divided into a fast and slow service, the freight service. This apart from private travel and transport. The two wheeled chariot drawn by two or four horses and the comparable cart for the country side, were the usual means of transport. The raeda (a Gallic word for a four wheeled wagon) was the precursor of the stagecoach. There was also a freight raeda drawn by eight horses during summer and ten during winter. It was not allowed to load it with more than a 1000 Roman pounds (about 330 kilos). Speed of transport varied from about 20 kilometers a day for freight service to 120 kilometers for the fastest postal service
In the Roman Empire, for the first time in history, a completely integrated system of roads was constructed and of cities intricately connected. The most important goal of these roads was the facilitation of movement for the military apparatus and for carrying out the administration. Transport of wheat and other big loads was almost always accomplished with simple boats, since transportation over land was too cumbersome and therefore too expensive.
The chariot was fast enough to guarantee a relatively quick form of communication, if at least a reasonably smooth surface could be realized. The Romans accomplished this through making the lower layer of the road dry and then by the laying of flat stones. Only relatively few roads were wide enough for two transport wagons. In fact many of them were quite narrow even for a single wagon. However a relatively great number of roads were capable of accommodating two chariots next to each other.
Another reason why the roads were mainly suitable for travel on foot and for horses by themselves, was that the Romans were not particularly successful in inventing a useful turning system for the wheels. They shared the use of oxen with other southern cultures and knew how to employ their strength. For this they availed themselves first of the horn yoke and subsequently of the shoulder yoke.
But they developed no technique for wagons with two or four wheels. Apparently the wheels were simply fixed to the axles. This meant that in a curve the other wheel was dragged along. Moreover, so historians think, the axles were stuck to the frame so that, when steering, the wagon was forced into the right direction rather than properly turned. Only the Celts had discovered how to make a proper swivel axle for the front. But the Romans did have greased iron axle bushings.