How did early Christians forge a Sunday, a Lord’s Day in a pagan culture? Somehow they maintained the rhythm of the week–and that may be no small feat, considering the week was a Jewish invention and not something followed in the greater Roman Empire. I would assume every day was a work day, and the aristocracy grabbed what leisure they could on the foundation of slaves, children, women, and others that could be exploited.
22. In those early Christian times, the weekly rhythm of days was generally not part of life in the regions where the Gospel spread, and the festive days of the Greek and Roman calendars did not coincide with the Christian Sunday. For Christians, therefore, it was very difficult to observe the Lord’s Day on a set day each week. This explains why the faithful had to gather before sunrise.(Cf. ibid. In reference to Pliny’s letter, Tertullian also recalls the coetus antelucani inApologeticum 2, 6: CCL 1, 88; De Corona 3, 3: CCL 2, 1043) Yet fidelity to the weekly rhythm became the norm, since it was based upon the New Testament and was tied to Old Testament revelation. This is eagerly underscored by the Apologists and the Fathers of the Church in their writings and preaching where, in speaking of the Paschal Mystery, they use the same Scriptural texts which, according to the witness of Saint Luke (cf. 24:27, 44-47), the Risen Christ himself would have explained to the disciples. In the light of these texts, the celebration of the day of the Resurrection acquired a doctrinal and symbolic value capable of expressing the entire Christian mystery in all its newness.
And that celebration would have included an element of liberation as well. The Vatican site has Dies Domini in its entirety.