Byzantium was an ancient Greek city, founded by colonists from Megara in 667 BC and named after their king Byzantas. The name "Byzantium" is a Latinization of the original Greek name Byzantion.
After siding with Pescennius Niger against the victorious Septimius Severus the city was besieged and suffered extensive damage in AD 186. Byzantium was rebuilt by the now Roman Emperor Septimius Severus and quickly regained its previous prosperity. The location of Byzantium attracted Constantine the Great who, in AD 330, refounded it as Nova Roma or Constantinoupolis (Constantinople) after a prophetic dream was said to have identified the location of the city.
Of course it did not take a prophet to see that this combination of imperialism and location would play an important role as the crossing point between two continents (Europe and Asia), and later a magnet for Africa and others as well, in terms of commerce, culture, diplomacy and strategy. At a strategic position, Constantinoupolis was able to control the route between Asia and Europe, as well as the passage from the Mediterranean Sea to the Euxinos Pontus (Black Sea).
In 1453 the city fell to the Ottoman Turks, and it has remained a part of Turkey to the present day.
In the 20th century the city was renamed Istanbul.
See also: Roman Empire, Roman Emperors, Constantinople, List of Byzantine Empire-related topics, Byzantine architecture, Byzantine Empire, and Byzantine Emperors.