Istanbul is the most-populous city of Turkey, serving as the place of residence of over 18% of the county's inhabitants. Istanbul is a transcontinental city in Europe and Asia, located between the Black Sea and the Sea of Marmara in northwestern Turkey, 64.7% of whose residents live on the European and 35.3% on the Asian side. Within city limits, Istanbul has an area of between 1166 and 1830 km2, it is the administrative center of the Istanbul metropolitan municipality (coterminous with Istanbul Province), which covers an area of 5343 km2, both areas hosting a population of around 14 million residents. Istanbul is one of the world’s most populous cities and ranks as world's 5th largest city proper, dropping the rank to the 24th place as an urban area and to the 18th place as a metro area due to a minor difference between the population within city limits and the agglomeration.
The area had been settled by Thracians in the late 6th millennium BC, to establish the city now known as Istanbul under the name Ligos around 3 millennia ago, which developed to become one of the most significant cities in history. The town saw the presence of Phoenicia, Ancient Greece, Ancient Persia and Ancient Rome, the city was renamed and called Byzantium (Βυζάντιον Byzántion) for nearly a millennia. Following its renaming to Constantinople in 330 AD, the city served as an imperial capital for the Roman (476–1204 and 1261–1453), the Latin (1204–1261), and the Ottoman (1453–1922) empires, when it became the largest city in the world. It was instrumental in the advancement of Christianity during Roman and Byzantine times, before the Ottomans conquered ciry in 1453 and transformed it into an Islamic stronghold and the seat of the Ottoman Caliphate.
Istanbul's strategic position along the historic Silk Road, rail networks to Europe and the Middle East, 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 Turkish 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.
Arts festivals were established at the end of the 20th century, while infrastructure improvements have produced a complex transportation network.
Approximately 11.6 million foreign visitors arrived in Istanbul in 2012, two years after it was named a European Capital of Culture, making the city the world's fifth-most-popular tourist destination. The city's biggest draw remains its historic center, partially listed as a UNESCO World Heritage Site, and it’s cultural and entertainment hub can be found across the city's natural harbor, the Golden Horn, in the beyoglu district. Considered a global city, Istanbul is one of the fastest-growing metropolitan economies in the world. It hosts the headquarters of many Turkish.