The Earliest Roads. In ancient Mesopotamia, people and goods traveled either overland or by water. On land, people usually walked, while goods were likely to be carried on pack animals or in wheeled vehicles—wagons or carts— drawn by oxen or donkeys. A network of paths stretched across the countryside between trading centers. Whereas people and animals might be able to walk over quite uneven or steep terrain, wheeled vehicles, in regular use since the early third millennium B.C.E., required a surface free of obstructions, sufficiently firm for the wheels not to become stuck, and not too steep for a draft animal to pull its load. Thus, using wheeled transport required that paths be cleared of obstacles, leveled, and packed firm; and they had to be maintained in that condition. The trace of any path, especially one intended for...