The Valens Aqueduct

The Valens Aqueduct was believed to have been built by the Roman Emperor Valens in the late 4th century AD, whose name is borne by the aqueduct. It was restored by several Ottoman Sultans later, and is one of the most important landmarks of the city. The Valens aqueduct, which originally got its water from the slopes of the hills between Kağıthane and the Sea of Marmara, was merely one of the terminal points of a complex system of aqueducts and canals. The total length of the network exceeds 250 km, the longest such system of Antiquity that stretched throughout the hill-country of Thrace and provided the capital with water.
The aqueduct of Valens had a length of 971 m and a maximum height of 29 m with a constant slope of 1:1000. Except for a bend to allow the construction of the Fatih Mosque, the aqueduct runs perfectly straight. The aqueduct stands in Istanbul, in the quarter of Fatih, and spans the valley between the hills occupied today by the Istanbul University and the Fatih Mosque. The surviving section is 921 m long, about 50 m less than the original length.