One megacity, two continents, four imperial capitals
Istanbul, Turkey’s largest city, holds over fifteen million people—about eighteen percent of the nation—and straddles the Bosphorus between Europe and Asia. From Megarian Byzantium in the seventh century BCE through Constantinople to Ottoman capital, it ruled four empires across nearly sixteen centuries before Ankara took the republican seat.
Greek colonists from Megara founded Byzantium around 657 BCE on Sarayburnu; Neolithic finds push peninsula settlement to the sixth millennium BCE. Constantine refounded it as New Rome in 324 and proclaimed it imperial capital on 11 May 330. Hagia Sophia under Justinian stayed the world’s largest cathedral for a millennium. Medieval Constantinople was often Europe’s largest, wealthiest city and a cradle of Orthodox civilisation—until the Fourth Crusade sacked it in 1204, dropping population toward a hundred thousand from earlier peaks near half a million.
Ottoman conquest came on 29 May 1453 after a fifty-five-day siege that killed Constantine XI. Mehmed II converted Hagia Sophia into an imperial mosque, claimed the title Kayser-i Rûm, and rebuilt the battered town with a new palace, the covered market still known as the Grand Bazaar, and more than a dozen mosques. The everyday name İstanbul likely grew from Greek eis tḕn Pólin—“to the city”—and entered official Ottoman use between the late seventeenth and eighteenth centuries; coinage showed Islambol from 1730 under Mahmud I. Western languages clung to Constantinople into the 1930s.
Today roughly two-thirds of residents live on the European side. The historic centre is UNESCO-listed; the metro area generates about thirty percent of Turkey’s economy and ranked fifth most-visited city worldwide in a 2025 Euromonitor list. Alpha-global status, two international airports, and football giants Galatasaray, Fenerbahçe, and Beşiktaş share the skyline with earthquake risk from the nearby North Anatolian Fault. Silk Road, rail, and the sole sea link between Black Sea and Mediterranean still explain why migrants and capital keep pouring in.
Source: Istanbul
