water-conveyance structure built under the Roman emperor Trajan (reigned AD 98–117) and still in use; it carries water 10 miles (16 km) from the Frío River to the city of Segovia, Spain. One of the best-preserved Roman engineering works, it was built of some 24,000 dark-coloured Guadarrama granite blocks without the use of mortar. The aboveground portion is 2,388 feet (728 metres) long and consists of some 165 arches more than 30 feet (9 metres) high. In the centre a dip in the terrain necessitated two tiers of arches; there the structure stands 93.5 feet (28.5 metres) above ground level. The aqueduct was designated part of the Segovia World Heritage site in 1985.