Constantinople
Constantinople (; ) was the capital city of the Roman/Byzantine Empire (330–1204 and 1261–1453), and also of the brief Crusader state known as the Latin Empire (1204–1261), until finally falling to the Ottoman Empire (1453–1923). It was reinaugurated in 324 from ancient Byzantium as the new capital of the Roman Empire by Emperor Constantine the Great, after whom it was named, and dedicated on 11 May 330. The city was located in what is now the European side and the core of modern Istanbul.
Europe
The empire continued to expand under emperors such as Antoninus Pius and Marcus Aurelius, who spent time on the Empire's northern border fighting Germanic, Pictish and Scottish tribes. The Empire began to decline in the 3rd century, particularly in the west. Christianity was legalised by Constantine I in 313 AD after three centuries of imperial persecution. Constantine also permanently moved the capital of the empire from Rome to the city of Byzantium, which was renamed Constantinople in his honour (modern-day Istanbul) in 330 AD. Christianity became the sole official religion of the empire in 380 AD, and in 391-392 AD, the emperor Theodosius outlawed pagan religions. This is sometimes considered to mark the end of antiquity; alternatively antiquity is considered to end with the fall of the Western Roman Empire in 476 AD; the closure of the pagan Platonic Academy of Athens in 529 AD; or the rise of Islam in the early 7th century AD.