Constantine the Great dedicates the much-expanded and rebuilt city of Byzantium, changing its name to New Rome and declaring it the new capital of the Eastern Roman Empire.

Constantine I, also known as Constantine the Great, was a Roman emperor from AD 306 to 337 and the first Roman emperor to convert to Christianity. He played a pivotal role in elevating the status of Christianity in Rome, decriminalising Christian practice and ceasing Christian persecution. This was a turning point in the Christianisation of the Roman Empire. He founded the city of Constantinople and made it the capital of the Empire, which it remained for over a millennium.

Byzantium or Byzantion was an ancient Greek city in classical antiquity that became known as Constantinople in late antiquity and Istanbul today. The Greek name Byzantion and its Latinization Byzantium continued to be used as a name of Constantinople sporadically and to varying degrees during the thousand-year existence of the Eastern Roman Empire, which also became known by the former name of the city as the Byzantine Empire. Byzantium was colonized by Greeks from Megara in the 7th century BCE and remained primarily Greek-speaking until its conquest by the Ottoman Empire in 1453 CE.

May 11 is the 131st day of the year in the Gregorian calendar; 234 days remain until the end of the year.