A long-distance waterway that brought water to Istanbul from the Belgrade forests in the north of the city. Construction took place between 1554 and 1563. The system was 55 km long and consisted of 33 aqueducts of various sizes.

'Kırkçeşme' refers to the forty fountains installed by Mehmed II when he restored the Cebeciköy line (previously part of the Hadrian Waterway) that went as far as the valley of the aqueduct bridge of Valens (Bozdoğan Kemeri) where the fountains were built. The installation is celebrated by Tursun Bey.

It is with the expansion under Suleiman the Magnificent's architect Mimar Sinan that the system fully matured. It was supplied by water from the Forest of Belgrade (Kemerburgaz area) through an extended Cebeciköy line that had been previously renovated by Mehmed II. This revitalised system was realised to support the surviving Byzantine water supply (Crow et al., 2008, p. 23).