The ancient sources record an earlier waterway of Hadrian constructed for the city of Byzantium. Its primary recipients were the Imperial Palace and the Baths of Achilles at the Strategion (ancient acropolis of Byzantium, now Topkapı Palace) (Crow et al., 2008, 10). The Hadrianic channel may have had a similar gradient to the later Valens channel (1 in 1,000).
If we relate the known topography to the two separate lines defined in the historical sources, it becomes apparent that:
One line was needed to supply the lower east end of the promontory (c. 30 m above sea level).
A second was needed to provide for new developments on the hills west of the Forum of Constantine.
These can be identified as the lower, Hadrianic line and the later and higher elevation of the Valens waterway, still defined in the city by the 971 m long Valens Aqueduct bridge/Bozdoğan Kemeri (now 50 meters missing?). The lower Hadrianic line provided water for the ancient city between the First and Second Hills. Earlier discussions of the water supply system within the city have suggested that the Valens Aqueduct bridge/Bozdoğan Kemeri, which crosses the valley between the Third and Fourth Hills, represents the line of the Hadrianic waterway, supplied from springs west of the city at Halkalı and associated with the bridge at Ma’zulkemer. (Crow et al., 2008, p. 13; cf. Çeçen 1996a, p. 129 suggested that the aqueduct bridge was a rebuilding by Valens of Hadrian’s original bridge). Cebiciköy and the Belgrade Forest most likely served as the most important sources for the Hadrian Waterway (Crow et al., 2008, p. 115).
The trajectory of the Hadrianic line can be followed between the Land Walls and Yerebatan Sarayı, alongside the hillsides (altitude c. 30 m).
By law, citizens were forbidden to tap water from the aqueduct for their own use: CIC (Justinianus) 11.42.6.
During the mid-10th century, the Hadrian Waterway regained its importance as the emperors moved from the Imperial Palace to Blachernai, which could be fed by the lower line. Andronikos I (r. 1183-1185) rebuilt an underground channel leading to the 'agora'.