321
Constantine makes Sunday the official day of rest
For a long time early Christianity debated the proper day for the Sabbath: Saturday, to follow the Jewish tradition; or Sunday, the day of the Resurrection. Standardization only occurred in the 4th century when the faith became legally recognized and the royal family of the Roman empire converted.
On March 7, 321 the emperor Constantine decreed that Sunday would be the universal day of rest throughout the Roman world:
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 so suitable for grain-sowing or vine-planting; lest by neglecting the proper moment for such operations the bounty of heaven should be lost.
Some claim that Constantine’s move was not directed so much by his new-found Christianity but by his long-standing devotion to the imperial sun-god cult of Sol Invictus. Coins bearing this image continued to be minted until 325.
This law was not immediately obeyed. The fact that the Council of Laodicea in 363 had to prohibit the Saturday Sabbath and demand Sunday rest meant that there was still the desire in some Christian communities to cling to the Jewish practice.