Byzantium (Greek: Βυζάντιον) was an ancient Greek city, which, according to legend, was founded by Greek colonists from Megara in 667 BC and named after their king Byzas or Byzantas (Βύζας or Βύζαντας in Greek). The name "Byzantium" is a Latinization of the original name Byzantion. The city is what later evolved to be the center of the Byzantine Empire, (the Greek-speaking Roman Empire of late Antiquity and the Middle Ages) with the name Constantinople. After the fall of Constantinople to the Ottoman Empire, the city became known as Istanbul to the Ottoman Turks, but that didn't become the official name of the city until 1930.

Byzantium! is a BBC Books original novel written by Keith Topping and based on the long-running British science fiction television series Doctor Who. It features the First Doctor, Ian, Barbara, and Vicki.