The Valens aqueduct (elsewhere I write aquaduct, once again proving I am not a native English speaker). It dates from 375 ot thereabouts. Unlike what one can see elsewhere (Rome, for instance) the water was let into the city underground, after having been diverted from streams in the surrounding hills, and the aqueduct did not start until about where we now find Fatih Mosque. The aqueduct let it across the valley, on to approximately the Beyazit Square. There a large cistern collected it, from which it was further distributed. The aqueduct has lost only some 100 meters of its length (now 900) and at its maximum is 20 metres high.
On its north side there was some small scale industry, producing kitchen furniture in hammered copper. Some of it is shipped abroad, and it was of high artistic quality.
This particular one should be in Köln, Germany by now.