“It was a Sunday afternoon, wet and cheerless; and a duller spectacle this earth of ours has not to show than a rainy Sunday in London.” ( Thomas De Quincey)
7 March 321 CE: Today, 1.692 years ago, Emperor Constantine the Great invented Sundays.
Even though the Battle of the Milvian Bridge and Constantine’s vision of the cross in whose sign he conquered already were a thing of the past for almost a decade, the emperor still followed the Cult of the "Unconquered Sun", Sol Invictus, as his predecessors did since the days of Septimius Severus mid of the 3rd century.
Constantine even claimed the sun as being his companion, SOLI INVICTO COMITI, and took good care to align the orb as well as the favours of the Roman soldier’s god Mithras, with his rule. He remained High Priest of both cults unto his deathbed. What made him decree a weekly feast day for the sun is uncertain, mere piety and devotion is not likely though. Favouritism with the subjects of his crumbling empire on religious grounds is a more probable. Constantine decreed:
“On the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed. In the country however persons engaged in agriculture may freely and lawfully continue their pursuits because it often happens that another day is not suitable for grain-sowing or vine planting; lest by neglecting the proper moment for such operations the bounty of heaven should be lost.”
Sunday as day of rest was incorporated into the Christian calendar as early as 354 CE, probably together with Sol Invictus’ holy day, the rebirth of the sun, December 25th as the day of the birth of Jesus Christ.
The basrelief above shows Sol Invictus shining benevolently on Mithras overcoming evil personified in the bull, the Tauroctony. (Musei Vaticani, ca 4th century)