(Derived from Greek: eis ten polein = "to the city" / "in the city")
Since 1926, the official name of the largest city of Turkey. Istanbul was formerly the capital of the Ottoman Empire, and known as Constantinople, Byzantium/Byzantion.
Founded ca. 660 BCE as a colony of the Greek city state of Megara, Istanbul was originally known as Byzantion. Located on the Bosporus, the city soon became a focal point for trade between the Greeks and the neighbouring peoples of Thrace, Scythia and the Greek colonies along the coasts of the Black Sea.
Byzantion was a member of the Delian League in the 400s BCE, and of the Second Athenian Sea League until 357 BCE. In Hellenistic times, the city was subject to Macedon.
In Roman times, the city supported the pretender Pescennius Niger against the Roman emperor Septimius Severus, but was conquered and laid waste after a grueling two-year-long siege, 193-195. The city was rebuilt and refounded in 330, under Constantine the Great, who made it the new capital of the Roman Empire, under the name Nova Roma - a name that was quickly supplanted by the unofficial name Constantinople (Greek: Constantinopolis, "Constantine's city").
When the West Roman Empire declined, Constantinople remained the capital of the East Roman Empire (now known as the Byzantine Empire). The city was greatly expanded and surrounded by massive fortifications. Constantinople became the most fortified city in Europe, if not in the world.
All the fortifications failed to prevent the capture and occupation of the city by a Crusader army, from 1204 to 1261. The city never quite recovered its strength after the occupation, and its conquest in 1453, by the Turkish Sultan Mehmed II, was almost an anticlimax.
From 1453 until 1923, Constantinople was the capital of the Ottoman Empire. Until ca. 1600, the city was also the economic and military hub of the empire.
With the dissolution of the Ottoman sultanate in 1923, by Kemal Atatürk, the capital was moved to Ankara. In 1926, the city's name was changed to Istanbul (reflecting a long-standing usage). Over the following decades, Istanbul and its surroundings has undergone a radical process of industrialisation and urbanisation (in particular, the city has absorbed many migrants from Anatolia).