Istanbul is the largest city in Turkey, largest city proper and second largest metropolitan area in Europe, and fourth largest city proper in the world with a population of 12.6 million. Istanbul is also a megacity, as well as the cultural and financial center of Turkey. The city covers 27 districts of the Istanbul province. It is located on the Bosphorus Strait and encompasses the natural harbor known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) sides of the Bosphorus, and is thereby the only metropolis in the world that is situated on two continents. In its long history, Istanbul has served as the capital city of the united Roman Empire and the East Roman (Byzantine) Empire, the Latin Empire, and the Ottoman Empire. The city was chosen as joint European Capital of Culture for 2010. The historic areas of Istanbul were added to the UNESCO World Heritage List in 1985. The modern Turkish name Istanbul or colloquial has been used to describe this city, 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. In English the name is usually written Istanbul. In modern Turkish the name is written Istanbul because in the Turkish alphabet dotted i (capital) is a different letter from dotless (capital I). Byzantium is the first known name of the city. In 667 B.C., this Doric colony was founded by settlers from the city-state of Megara, and they named the colony after their king Byzas. 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. 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 28 March 1930, the Turkish authorities officially requested foreigners to adopt Istanbul as the sole name also in their own languages.