You Catholics got Sunday from Mithraism.

The Catholic Answers

We did not. Sunday may have been the day celebrated in honor of Mithra. But this was not the reason for its selection by Christians. There is as much connection between the Christian choice of Sunday and Mithraism as there is between the fact that the Jews observed Saturday and the derivation of the word in English from Saturn. Had the Church chosen Wednesday for some reason of her own, you would alter your charge and cry in triumph, “Ah! The day sacred to Wodin.”

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty