But when Rome collapsed in the fifth century and the Middle Ages began, direct trade of spices stopped, and so did that kind of hands-on knowledge of travel and geography.
Dependence on long-distance trade also meant that the great empires of the Middle East were built both literally and figuratively on shifting sand.
对长途贸易的依赖也意味着，伟大的中东帝国无论是实际上还是象征意义上，都是建立在流沙之上的。
3
Trade was the mainstay of the urban economy in the Middle East, as caravans negotiated the surrounding desert, restricted only by access to water and by mountain ranges.