Who ruled Istanbul?

Istanbul stands on both shores of the Bosphorus, the narrow strait that joins the Black Sea to the Sea of Marmara and divides Europe from Asia. Its historic core is a hilly triangle of land between the Marmara and the Golden Horn, a long natural harbour, protected by water on two sides and by walls on the third. Whoever held this site controlled the passage between two seas and two continents, and for some sixteen centuries it was the capital of two great empires, first as Byzantium and Constantinople, then as Istanbul.

Greek colonists from Megara founded Byzantion on the European shore in about 657 BCE, according to tradition. The city fell under the Achaemenid Persian Empire in the late 6th century BCE, returned to Greek hands after the Persian wars, and later came under Rome. After the emperor Septimius Severus sacked it in 196 CE for backing a rival, he rebuilt it on a larger plan.

The decisive moment came when Constantine I chose Byzantium as a new imperial capital and dedicated it in 330 CE as Constantinople. In the 5th century the Theodosian Walls were built across the landward side, and they held off attackers for a thousand years. Under Justinian I the city survived the Nika riots of 532 and gained the great church of Hagia Sophia, completed in 537. As capital of the Byzantine Empire, Constantinople was for centuries the largest and richest city in Europe. It resisted sieges by Avars and Persians in 626 and by Arab forces in the 670s and in 717 and 718. The worst blow came from fellow Christians: the army of the Fourth Crusade sacked the city in 1204 and set up a Latin empire, which lasted until the Byzantines retook Constantinople in 1261.

By the 15th century the shrunken city was surrounded by Ottoman territory. On 29 May 1453 the young sultan Mehmed II took it after a siege of about seven weeks, ending the Byzantine Empire in the fall of Constantinople. Mehmed repopulated the city with Muslims, Christians and Jews from across his realm, turned Hagia Sophia into a mosque and began the Topkapı Palace. Under Suleiman the Magnificent in the 16th century the architect Sinan filled the skyline with domes and minarets, including the Süleymaniye Mosque. As capital of the Ottoman Empire, the city was home to large Greek, Armenian and Jewish communities alongside its Muslim majority, and Ottomans used "Istanbul" as well as "Konstantiniyye" for its name.

In the 19th century reforming sultans built new palaces along the Bosphorus, and railways, steamships and a bridge across the Golden Horn tied the city to Europe. After the Ottoman defeat in the First World War, Allied troops occupied Istanbul from 1918 to 1923.

The nationalist government of Mustafa Kemal Atatürk made Ankara the capital of the new Republic of Turkey in 1923, and Istanbul lost its political role. Its minority communities shrank sharply through population exchanges, the anti-Greek riots of September 1955 and later expulsions. From the 1950s migration from Anatolia drove explosive growth. Bridges over the Bosphorus opened in 1973, 1988 and 2016, and a rail tunnel beneath it in 2013. Istanbul is now Turkey's largest city and economic centre, with about 15.7 million people.