Aqquaduct of Valens was a Roman aqueduct system built in the late 4th century AD, to supply Constantinople – the capital of the Eastern Roman Empire. Construction of the aqueduct began during the reign of the Roman emperor Constantius II (r. 337–361) and was completed in 373 by the Emperor Valens (r. 364–378). The aqueduct remained in use for many centuries. It was extended and maintained by the Byzantines and the Ottomans.