Changes

While highways and royal roads developed by the late 2nd and early 1st millennium BCE, such roads were not paved and often were little more than pathways serviced by rest stations, stables, and inns. Such roads became difficult to travel in wet conditions, making them less than ideal in the wet season. In the Roman Period, road engineering reached a new level. Now, roads were built with deeper foundations and underlain with crushed gravel. This helped to drain roads as water could go through rather than be trapped in the clay. Additionally, paved roads were developed on the most important highways. <ref>For more on Roman engineered roads, see: Nardo, D. (2015). Roman roads and aqueducts. San Diego, CA: ReferencePoint Press.</ref> This included using large capstones. Pavement gave roads additional speed since wheeled carts and chariots could move more quickly in pavement than in dirt roads. Sometimes these roads were construct with multiple layers so that water could be drained and pavement would provide for additional speed. Some of these roads are still used or are visible today. Road technology in Europe, in fact, did not improve to any great extent from Roman designs until about the 18th century CE.

In the Islamic world, innovations were developed in the types of pavement used. Baghdad developed the use of tar that derived from pitch or bitumen. <ref>For more on Islamic roads, see: Bobrick, B. (2012). The caliph’s splendor: Islam and the West in the golden age of Baghdad (1st Simon & Schuster hardcover ed). New York: Simon & Schuster.</ref> In fact, this was already present in ancient Babylonian cities but was not widely used. The use of bitumen as a type of tar was a forerunner of tar and asphalt roads that are today widely used. Bitumen was relatively easily available and its waterproofing qualities meant that streets could become relative dry quickly and remain mud free.

By the 18th century, road technologies once again began to improve as engineering was more greatly utilized. Concepts of drainage now led to roads being created that were crested so that water can run to the sides and be drained in areas away from the main road to keep roads dry. Specific stones now were utilized for their qualities, such as thickness and durability. Road maintainers were employed to keep sections of roads well maintained. By the early 19th century, road paving using a combination of dirt and stone proved to be useful for road durability. <ref>For more on how early industrialization improved roads, see: Guildi, E.J. 2001. The Road to Rule: The Expansion of the British Road Network, 1726--1848. Proquest. </ref> This remained the main type of road until 1901, when tarmac was utilized to pave roads. The idea was similar to what was used in the Medieval Islamic period; however, tar was mixed with aggregate material to create a more mixed product than pure tar from bitumen. This mixture became the type of surface we today see in most roads.