this is about us page The city served as an imperial capital for almost 1600 years: during the Roman/Byzantine (330–1204), Latin (1204–1261), late Byzantine (1261–1453), and Ottoman (1453–1922) empires.^[12] The city played a key role in the advancement of Christianity during Roman/Byzantine times, hosting four (including Chalcedon (Kadıköy) on the Asian side) of the first seven ecumenical councils (all of which were in present-day Turkey) before its transformation to an Islamic stronghold following the Fall of Constantinople in 1453 CE—especially after becoming the seat of the Ottoman Caliphate in 1517.^[13]