The Valens Aqueduct (Bozdoğan Kemeri, "Bow of the Grey Falcon") is part of an extensive old water pipeline in the Istanbul districts of Saraçhane and Zeyrek that supplied the city with water. It originally extended a little more than a kilometre between the two hills of Fatih and Eminönü in the European part of the city. Today only about 800 meters of it are left and span the Atatürk Bulvarı.
The parts that no longer exist were destroyed by attacks and earthquakes and restored again and again, for the last time in 1697. The construction of the aqueduct began under Emperor Constantine the Great, during his reign from 306 to 337 and was completed in 378 under Emperor Valens. Hence the name Valens Aqueduct.
In 766 it was renovated by Emperor Constantine V with enormous personnel expenditure. The drinking water coming from Alibeyköy was distributed through the aqueduct to all places in the town. The building has two floors and consists of superimposed brick arches, the height of which varies between 18.5 and 26.5 metres.

Istanbul was founded around the year 660 BC by Doric Greeks from Megara, Argos and Corinth under the name Byzantion. For almost 1600 years it served successively as the capital of the Roman, Byzantine and Ottoman Empires.
Due to its favourable location on the European shore of the Bosporus, on the eastern tip of a peninsula between the Sea of Marmara and the Golden Horn, Byzantium was expanded from 326 to 330 by Emperor Constantine I to become the new capital of the Roman Empire and was subsequently called Constantinople.
After the conquest of the city and the Byzantine Empire named after it by the Turks, it was the capital of the Ottoman Empire from 1453 to 1923, from which today's Istanbul emerged. Under Emperor Vespasian (69-79), Byzantium was incorporated into the Roman Empire as part of the province of Bithynia et Pontus.
After the city had experienced an economic boom since the 4th century BC due to the control of maritime trade, its growth was slowed down by the tax liability towards the Roman governor. Septimius Severus had the city destroyed in 196 AD as punishment for supporting his rival Pescennius Niger, but it was rebuilt through Caracalla's intercession. In 258 Byzantium was plundered and destroyed by the Goths.
On 11 May 330 AD, the Roman Emperor Constantine the Great made it his main residence, generously extended it and officially named it Nova Roma. A little later, however, she was given the new name Constantinopolis.

In 1876 the name of the capital as Istanbul was included in the new constitution, where it was stated in Article 2:
"Devlet-i Osmaniyenin payitahtı Istanbul şehridir / The capital of the Ottoman state is the city of Istanbul"
On 28 March 1930, in the early days of the Republic, İstanbul became the official name of the entire city. Since the city has been called so in Ottoman scriptures and in Turkish vernacular for a long time, this was actually not a renaming, but an approximation to a long common usage. In most European countries, the term Istanbul gradually replaced the term Constantinople or its variants.