Further information: Names of Istanbul
The modern Turkish name İstanbul can be attested, in a range of different variants, from as far back as the 10th century; it has been the common name for the city in normal Turkish speech since before the conquest of 1453. Etymologically, it derives from the Greek phrase "εἰς τὴν Πόλιν" or in the Aegean dialect "εἰς τὰν Πόλιν" (modern Greek "στην Πόλι"), which means "in the city", "to the city" or "downtown".
Byzantium is the first known name of the city. When Roman emperor Constantine I (Constantine the Great) made the city the new eastern capital of the Roman Empire on May 11, 330, he conferred on it the name Nova Roma ("New Rome"). Constantinople ("City of Constantine") was the name by which the city became instead more widely known. It is first attested in official use under emperor Theodosius II (408450). It remained the principal official name of the city throughout the Byzantine period, and the most common name used for it in the West until the early 20th century.
The city has also been nicknamed "The City on Seven Hills" because the historic peninsula, the oldest part of the city, was built on seven hills (just like Rome), each of which bears a historic mosque. The hills are represented in the city's emblem with seven triangles, above which rise four minarets. Two of many other old nicknames of Istanbul are Vasilevousa Polis (the Queen of Cities), which rose from the city's importance and wealth throughout the Middle Ages; and Dersaadet, originally Der-i Saadet (the Door to Happiness) which was first used towards the end of 19th century and is still remembered today.
With the Turkish Postal Service Law of March 28, 1930, the Turkish authorities officially requested foreigners to adopt Istanbul as the sole name also in their own languages.