Canals—manmade waterways—divert water from natural sources to facilitate transportation, irrigate or drain land, and supply water. Irrigation canals were a feature of most ancient civilizations. The Nahrwan Canal, l85 mi. (300 km) long, was built between the Tigris and Euphrates rivers circa 2400 b.c., and Egypt's pharoahs linked the Mediterranean and Red seas with a canal that the Romans later restored and used for shipping. China built the initial stretch of its Grand Canal in 6l0 a.d., a waterway 600 mi. (l000 km) in length at its completion. Canal systems for transportation were not widespread in Europe until the 1600s and 1700s. The first network came into use in the Netherlands, which had adapted drainage canals to handle boats by the thirteenth and fourteenth centuries. France's Canal du Midi linked the Atlantic and Mediterranean by l68l. Cargo boats...