Segovia, Spain
Segovia was a Roman Military base and needed water. Emperor Trajan's engineers built a nine-mile aqueduct to channel water from the Rio Frio to the city, culminating at the Roman castle which is the Alcazar. The famous and exposed section of the 2000 year old aqueduct is 2,500 feet long and 100 feet high, has 118 arches, was made from 20,000 granite blocks without mortar, and can still carry a stream of water.