@ajp_sydney, the old online Catholic Encyclopedia has some information under the heading “Sunday”, such as this:
St. Justin is the first
Christian writer to call the day Sunday (I Apol., lxvii) in the celebrated passage in which he describes the worship offered by the early
Christians on that day to
God. The fact that they met together and offered public worship on Sunday necessitated a certain rest from work on that day. However,
Tertullian (202) is the first writer who expressly mentions the Sunday rest: “We, however (just as tradition has taught us), on the day of the
Lord’s Resurrection ought to guard not only against kneeling, but every posture and office of solicitude, deferring even our businesses lest we give any place to the
devil” (“De orat.”, xxiii; cf. “Ad nation.”, I, xiii; “Apolog.”, xvi).
These and similar indications show that during the first three centuries practice and tradition had
consecrated the Sunday to the public worship of
God by the hearing of the Mass and the resting from work. With the opening of the fourth century positive legislation, both
ecclesiastical and civil, began to make these
duties more definite. The Council of Elvira (300) decreed: “If anyone in the city neglects to come to church for three Sundays, let him be
excommunicated for a short time so that he may be corrected” (xxi). In the Apostolic Constitutions, which belong to the end of the fourth century, both the hearing of the Mass and the rest from work are prescribed, and the precept is attributed to the
Apostles. The express teaching of Christ and
St. Paul prevented the early
Christians from falling into the excesses of Jewish
Sabbatarianism in the observance of the Sunday, and yet we find St. Cæsarius of Arles in the sixth century teaching that the
holy Doctors of the Church had decreed that the whole glory of the Jewish
Sabbath had been transferred to the Sunday, and that
Christians must keep the Sunday holy in the same way as the
Jews had been commanded to keep holy the
Sabbath Day.
http://www.newadvent.org/cathen/14335a.htm