from Phillip Shaff’s, History of the Christian Chruch, Vol 3 Nicene and Post-Nicece Christianity. AD 311-600
17. The civil sanction of the observance of Sunday and other festivals of the church. The state, indeed, should not and cannot enforce this observance upon any one, but may undoubtedly and should prohibit the public disturbance and profanation of the Christian Sabbath, and protect the Christians in their right and duty of its proper observance. Constantine in 321 forbade the sitting of courts and all secular labor in towns on “the venerable day of the sun,” as he expresses himself, perhaps with reference at once to the sun-god, Apollo, and to Christ, the true Sun of righteousness; to his pagan and his Christian subjects. But he distinctly permitted the culture of farms and vineyards in the country, because frequently this could be attended to on no other day so well; though one would suppose that the hard-working peasantry were the very ones who most needed the day of rest. Soon afterward, in June, 321, he allowed the manumission of slaves on Sunday;as this, being an act of benevolence, was different from ordinary business, and might be altogether appropriate to the day of resurrection and redemption. According to Eusebius, Constantine also prohibited all military exercises on Sunday, and at the same time enjoined the observance of Friday in memory of the death of Christ.
Nay, he went so far, in well-meaning but mistaken zeal, as to require of his soldiers, even the pagan ones, the positive observance of Sunday, by pronouncing at a signal the following prayer, which they mechanically learned: “Thee alone we acknowledge as God; thee we confess as king; to thee we call as our helper; from thee we have received victories; through thee we have conquered enemies. Thee we thank for good received; from thee we hope for good to come. Thee we all most humbly beseech to keep our Constantine and his God-fearing sons through long life healthy and victorious.”Though this formula was held in a deistical generalness, yet the legal injunction of it lay clearly beyond the province of the civil power, trespassed on the rights of conscience, and unavoidably encouraged hypocrisy and empty formalism.
Later emperors declared the profanation of Sunday to be sacrilege, and prohibited also the collecting of taxes and private debts (368 and 386), and even theatrical and circus performances, on Sunday and the high festivals (386 and 425). But this interdiction of public amusements, on which a council of Carthage (399 or 401) with reason insisted, was probably never rigidly enforced, and was repeatedly supplanted by the opposite practice, which gradually prevailed all over Europe