The special honour which the faithful paid to the Sunday (], may have helped, later on, to produce the impression that the Christians had much in common with the worshippers of Mithras.
What more nearly concerns us here is the Jewish calendar, outlined in Leviticus 23.
The computation of time among the Jews was based primarily upon the lunar month.
In 1897, a remarkable discovery was made at Coligny in the department of Ain, France, when certain inscribed stone slabs were brought to light in which all are agreed in recognizing an ancient Celtic calendar, probably pre-Christian, though the precise interpretation of the details still remains a matter of lively controversy.
Again, both Greece and Rome possessed highly developed calendars, and the of Ovid, for example, preserve a detailed description in verse of the chief celebrations of the Roman year.
The Day of Atonement fell on 10 Tishri and the Feast of Tabernacles extended from the 14th to the 21st, with a sort of octave day on the 22nd, but these had no direct bearing on the calendar of the Christian Church.