Istanbul is the largest city in Turkey and the country's economic, cultural and historic center. The city straddles the Bosphorus strait, and lies in both Europe and Asia, with a population comprising 19% of the population of Turkey. Istanbul is the most populous city in Europe, and the world's fifteenth-largest city. Founded as Byzantion by Megarian colonists in 657 BCE, and renamed by Constantine the Great first as New Rome (Nova Roma) during the official dedication of the city as the new Roman capital in 330 CE, which he soon afterwards changed as Constantinople (Constantinopolis), the city grew in size and influence, becoming a beacon of the Silk Road and one of the most important cities in history. It served as an imperial capital for almost sixteen centuries, during the Roman/Byzantine (330–1204), Latin (1204–1261), Byzantine (1261–1453), and Ottoman (1453–1922) empires. It was instrumental in the advancement of Christianity during Roman and Byzantine times, before its transformation to an Islamic stronghold following the Fall of Constantinople in 1453 CE. In 1923, after the Turkish War of Independence, Ankara replaced the city as the capital of the newly formed Republic of Turkey. In 1930 the city's name was officially changed to Istanbul, an appellation Greek speakers used since the eleventh century to colloquially refer to the city. Over 13.4 million foreign visitors came to Istanbul in 2018, eight years after it was named a European Capital of Culture, making the city the world's fifth-most popular tourist destination. Istanbul is home to several UNESCO World Heritage Sites, and hosts the headquarters of numerous Turkish companies, accounting for more than thirty percent of the country's economy.
Istanbul is rated Alpha − by the Globalization and World Cities Research Network (GaWC) which evaluates and ranks the relationships between world cities in the context of globalisation. Alpha level cities are linked to major economic states and regions and into the world economy.
Istanbul is the #37 city in the world according to the Global Power City Index (GPCI) which evaluates and ranks the major cities of the world according to their magnetism, or their comprehensive power to attract people, capital, and enterprises from around the world. It does so through measuring six key functions: Economy, Research and Development, Cultural Interaction, Liveability, Environment, and Accessibility.
Istanbul is the #64 city in the world according to the Global Financial Centres Index (GFCI) which evaluates and ranks the competitiveness of the major financial centres of the world according to a wide range of criteria – Human Capital, Business, Finance, Infrastructure and Reputation.
Istanbul is ranked #41 by the Global Urban Competitiveness Report (GUCR) which evaluates and ranks world cities in the context of economic competitiveness. Istanbul is rated B by the Global Urban Competitiveness Report (GUCR) which evaluates and ranks world cities in the context of economic competitiveness. B cities are international hub cities. Istanbul was ranked #4 by the Nomad List which evaluates and ranks remote work hubs by cost, internet, fun and safety. Istanbul has a population of over 14,657,000 people. Istanbul also forms part of the Greater Istanbul metropolitan area which has a population of over 15,519,267 people.