Constantine I (c.272-337), Roman emperor. Born Flavius Valerius Constantinus, and later known as 'the Great', he was proclaimed emperor upon his father's death in 306. Following a power struggle he became emperor of both the Eastern and Western Roman Empires in 324. He then converted to Christianity and ended the persecution of Christians. In 326 he founded Constantinople (present-day Istanbul), which remained the capital of the Eastern Roman Empire (later the Byzantine Empire) until 1453. One of Constantine's reforms was to introduce the seven-day week in 320. Artwork from 'Histoire des Romains' (1883).