Introduction: Roads 101
What makes a good road, especially one that uses materials and processes from earlier times? There are a few principles that guide road design:
1) Good drainage. Keep the road dry. Think about when you walk on waterlogged soil. Your foot sinks into the mud. Walking is much easier on dry soil. The exception is a sand soil. Sand is actually easier to walk on when wet, as you find on the beach.
a. Drain surface by having a crown in the middle (middle is higher than sides) so water drains toward the sides.
b. Dig ditches on the sides and throw the soil up to the center of the road to create both drainage and a crown. Drain water to more than 5 feet below the surface.
c. If possible, have underdrainage by tile or something similar to drain the subsurface.
2) Seal the surface of the road, if possible. Keep ruts to a minimum. The surface layer should be strong enough to withstand the pounding from traffic. If a special surface is used, such as asphalt or stones, the surface is paved.
3) Sealing the surface requires a binder. Currently asphalt is used. Remember that in cold, wet climates like Europe there will be freeze and thaw cycles that can break a brittle binder like mortar and require repairs.
4) The subsoil under the road should be kept dry so that it will maintain its strength. Again, drainage and sealing are the keys to keeping the subsoil dry.
Roman Roads
The roads of ancient Rome are considered by some to be engineering marvels. Some of them have lasted 2000 years. However, from an engineering standpoint, the Roman road is not what laymen think it is.
Ancient Rome had very primitive technology, including its land transportation system. The key to understanding Roman roads is to understand their use of the horse. Ancient peoples did not know how to harness a horse. The harnesses they used cruelly leaned on the animal’s windpipe, so as a horse pulled harder it began to strangle itself. Consequently, a horse could only pull light vehicles such as chariots and carriages. It could not pull a freight wagon. Ox carts were too slow for transporting over long distances. For these reasons, freight went via pack animals.
The horse had a second problem. Roman horses were not shod, i.e. they did not have horseshoes. A driver had to be careful lest the horse’s hooves wear out.
Roman roads are described as the earliest example of stone-block pavement. In general, they were as follows from bottom to top
1) Trench 3 feet deep.
2) Base: one or two layers of large flat stones laid in mortar, about 15 inches.
3) Next a 9-inch course of small fragments of stone imbedded in mortar
4) Next a 6-inch layer of concrete
5) Pavement: closely jointed, irregularly shaped stones, about 6 inches thick. Near cities the top course was irregular blocks 12-15 inches thick, fitted with extreme accuracy and imbedded in cement.
This is sometimes described as a ‘masonry wall laid on its side’.
While it would not be apparent from archeological remains, there was probably a layer of 2-3 inches of topsoil to protect the horse’s feet from injury. If there was not, then the horse would slip on the pavement when it was wet. It would also wear its hooves out. In general, if there was no soil, the animals had to walk along the sides of the road. Since water was being drained from the road to the sides, they would be walking in mud.
The Roman road is remarkable chiefly for its expense. It costs 4 to 8 times as much as superior modern pavements. It was used chiefly for pack animals and foot traffic. It might be better described as a foot path. Traffic was light for such an expensive road. No effort was made to improve the roads over time. Apparently the Romans decided they were satisfactory and never bothered with them again.
The roads ran in straight lines up hills, which meant that the grades were too steep for wagons. The roads go to the highest point, probably so that army commanders could have a view of an approaching enemy. These roads were chiefly used for military purposes, particularly when built away from cities or in remote provinces. Trade did not travel on such roads.
Roads in the Dark Ages
In the early part of Dark Ages (500-1000) AD, roads were chiefly earth roads. The horse was properly shod and harnessed, so it could travel longer distances and pull without strangling itself. Earth roads are suited to rural areas; in 1890, for example, 95% of all roads in the US were earth roads. When dry, they are suitable for wagon traffic, as long as they are of earth (clay or loam) and not sand. A horse can pull a wagon with a two-ton load at a speed of 2.5 miles/hour on a dry earth road. Such roads are cheap to build and maintain. Maintenance costs go up as the traffic goes up; with twice the amount of traffic, twice the maintenance is required.
After 1000 AD, most of the wars that had been ravaging Western Europe ended. In the ensuing peace, cities started growing. After some experimentation, inexpensive cobblestone roads began to be built. This is just cobblestones on a bed of sand or natural soil. It has a low first cost and is serviceable; most cities in the US were paved with cobblestones throughout the 19th century.
Until the advent of the railroad, the cheapest way to have overland trade was on the river system. Compared to horse drawn wagons, a barge is very cheap to operate. Cities and ports are usually built near the mouths of navigable rivers, and the river was used to take goods down to the cities. In this case, the only roads needed would be the ones from farm or factory to a pier on the river. Goods were barged down the river, and sometimes the barge was sold or broken up for firewood. Goods going upriver could be paddled, poled or towed by a horse along a towpath on the side of the river. It was sometimes easier to portage around a stretch of rapids and keep paddling upriver. This technique was used, for example, by the French voyageurs of Canada in the 17th century. They paddled all over Western Canada with trade goods going out from Lake Superior and came back with furs. They portaged their big freighter canoes around the rapids and kept going.
Summary
Roman roads were built to enable armies to march from one area to another. The army used pack animals to move supplies. It did not use wagons; Romans could not use freight wagons because their harnesses strangled a horse when it tried to pull hard. Near cities, the roads were widened for civilian use.
Dark Age roads were practical and low-cost. The types of roads developed in the Dark Ages, earth roads and cobblestone roads, were also in use, with some refinement, in 19th century America. In the early part of the Dark Ages, a proper harness for horses was developed and adopted. Horseshoes, nailed to the hoof, were also adopted. This allowed the horse to be used for many more tasks such as plowing and pulling freight wagons.
The purpose of a road is to help move people and goods from one place to another place. From this viewpoint, roads from the Dark Ages are vastly superior to Roman roads. Roman roads are spectacular from an archeological viewpoint, but no one builds a road to impress archeologists.
Sources
Baker, Ira Osborn, A Treatise on Roads and Pavements, 2nd edition, 1914, John Wiley and Sons, Inc., New York, NY.
This is a civil engineering textbook on roads. It was written in 1914, and the 1st edition is from 1903, which means that the author was well acquainted with the problems of road building for horse-drawn vehicles. Many of the materials and methods available in ancient times were still being used. For example, gravel was just coming into wide use; previously crushed rock was not available because there were no rock crushers. For this reason, earth roads were in use. Most of the opinions on Roman roads, including expenses, are taken from Roads and Pavements.
Boardman, Fon W. Jr., Roads, 1958, Henry Z. Walck, Inc., New York, NY.
This is a short book for laymen. It is listed here because it has a woodcut showing cobblestone roads being laid in the 15th century.
