Istanbul is the largest city in Turkey, constituting the country's economic, cultural, and historical center. With a population of over 15 million, it is home to 18% of the population of Turkey. Istanbul is among the largest cities in Europe and in the world by population. It is a city on two continents; about two-thirds of its population live in Europe and the rest in Asia. Istanbul straddles the Bosphorus – one of the world's busiest waterways – in northwestern Turkey, between the Sea of Marmara and the Black Sea. Its area of 5,461 square kilometers (2,109 mi2) is coterminous with Istanbul Province. The city now known as Istanbul developed to become one of the most significant cities in history. Byzantium was founded on the Sarayburnu promontory by Greek colonists, potentially in the seventh century BC. Over nearly 16 centuries following its reestablishment as Constantinople in 330 AD, it served as the capital of three empires: the Roman Empire (later known as the Byzantine Empire, 330–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). It was instrumental in the advancement of Christianity during Roman and Byzantine times, before the Ottomans conquered the city in 1453 and transformed it into an Islamic stronghold and the seat of the last caliphate. Although the Republic of Turkey established its capital in Ankara, palaces and imperial mosques still line Istanbul's hills as visible reminders of the city's previous central role. The historic centre of Istanbul is a UNESCO World Heritage Site Istanbul's strategic position along the historic Silk Road, rail networks to Europe and West Asia, and the only sea route between the Black Sea and the Mediterranean have helped foster an eclectic populace, although less so since the establishment of the Republic in 1923. Overlooked for the new capital during the interwar period, the city has since regained much of its prominence. The population of the city has increased tenfold since the 1950s, as migrants from across Anatolia have flocked to the metropolis and city limits have expanded to accommodate them. The majority of Istanbul’s Turkish citizens are of ethnic Turkish origin, whereas ethnic Kurds represent the largest ethnic minority in the city. By the late twentieth century, a number of arts festivals had been established, and sustained infrastructure development led to the emergence of an extensive and multifaceted transportation network Considered an alpha global city, Istanbul accounts for about thirty percent of Turkey's economy. The Istanbul-İzmit area is one of the main industrial regions in Turkey. In 2024, Euromonitor International ranked Istanbul as the second most visited city in the world. Istanbul is home to two international airports, multiple ports, and numerous universities. It is among the top 100 science and technology clusters in the world. The city hosts a large part of Turkish football and sports in general, with clubs such as Galatasaray, Fenerbahçe and Beşiktaş. Istanbul is vulnerable to earthquakes as it is in close proximity to the North Anatolian Fault.

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