Decree of Sunday as Rest Day

Date: March 7, 321 • Location: Istanbul, Turkey

Emperor Constantine I decreed that Sunday, the day honoring the sun god Sol Invictus (disc pictured), would be the Roman day of rest.

Constantine I, also known as Constantine the Great, was 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 the Roman Empire, the Edict of Milan 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.