In the sixth century, the monk Dionysius Exeguus worked on the traditional Christian task of setting the dates for the celebration of Easter. He became increasingly uncomfortable about using the official dating system of his day. He therefore set about to calculate the date of the conception of Jesus, for him the appropriate reference point for dating the celebration of Easter. His system caught on quickly in Italy, but Charlemagne (742 or 743 to 814) is said to have been the first major ruler to