Rolling resistance is also the reason that some human civilizations didn't use wheels. During the Roman Empire, wheeled chariots were common in the Middle East and North Africa. However, when the Empire fell, wheels became less useful to the local people, who turned to camels to transport goods in the sandy desert climate. Stephen Jay Gould wrote about this strange fact of history in his book "Hen's Teeth and Horse's Toes". He wrote that without maintained roads, camels needed less human power and water than a cart pulled by oxen.