Istanbul was once known as Constantinople and Byzantium. Its commercial and historical centres, and two thirds of its population, are on the European side of the Bosphorus Strait (which separates Europe and Asia, there, a little further North you have make up other play play divisions). Istanbul is the world's 7th largest city proper. It was founded in around 660 BCE as Byzantion, and reestablished as the Imperial Capital of Rome by Constantine (the first Roman Emperor to claim conversion to Christianity) in 330 CE. It stayed the Capital of the Byzantine Empire after the fall of the West, and became the capital of the Ottoman Empire when it was conquered in 1453. The population of the city has increased tenfold since the 1950s, as migrants have come to the city in search of a better life.