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Constantine I. Historical portrait of the Roman emperor Constantine I, or the Great (274-337). Born Flavius Valerius Constantinus, 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 until 1453. One of his reforms was to introduce the seven-day week in 320. Previously the month had been the only repeating period in the Roman calendar, though other cultures used the week.
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