Istanbul - Wikipedia
Rise and fall Constantinople and Byzantine Empire. The Ottoman Empire and the Turkish Republic eras. Neighborhoods and districts. Religious and ethnic groups. Entertainment and leisure. International relations
Istanbul (/,Istaen’bUl/IST-an–BUUL, US; Turkish: Istanbul [is’tanbul] (listen), is the largest city of Turkey and serves as the country's cultural, economic, and historical hub. It lies in both Europe, Asia and the Bosporus Strait. The city has more than 15 million inhabitants, which is 19% of Turkey's total population. Istanbul is the 15th-largest and most populous city in Europe.
Byzantion (Byzantion), a Greek settlement from Megara, founded the city in 7th century BC.  Constantine the Great, the Roman Emperor, made it his imperial capital in 330 CE. He renamed it New Rome (Nova Roma), and Constantinople (Constantinopolis), after himself.  It grew in stature and influence and became a major city on the Silk Road.
It was the imperial capital of almost 1600 years. This included during the Roman/Byzantine (330-1204), Latin (1204-1261), late Byzantine (1261-1453), Ottoman (191453-1922), and Ottoman (191453-1922).  The city was a major player in the development of Christianity in Roman/Byzantine times. It hosted four of the seven first ecumenical councils, including Chalcedon (Kadikoy on the Asian side), before it became an Islamic stronghold in response to the fall of Constantinople in 1453 CE. This transformation occurred especially after it was made the seat of Ottoman Caliphate.