What Roman aqueduct in Istanbul supplied water to the city for centuries?

The Roman aqueduct in Istanbul that supplied the city for centuries is the Aqueduct of Valens.

The aqueduct formed part of the enormous water-supply network serving Constantinople, the capital of the Eastern Roman Empire. Construction began during the reign of Constantius II, and the system was completed under Emperor Valens in AD 368; a major inauguration followed in 373. Its name comes from Valens, even though he was not responsible for every stage of the project.

The first phase drew water from springs in Thrace and had channels extending about 268 kilometres. A later fifth-century phase added another 451 kilometres of conduits. Inside the city, the water fed reservoirs, baths, palaces, fountains, and cisterns, including the great underground storage system associated with Constantinople.

The surviving bridge is known in Turkish as Bozdoğan Kemeri. It once measured about 971 metres and reaches roughly 29 metres high. Byzantines and Ottomans repeatedly repaired and extended the supply network. Theodosian waterworks and earlier Hadrianic aqueducts also served the city, but the landmark traditionally identified by this name is the Aqueduct of Valens.