Why was January 1, 4713 B.C. chosen as the starting point? According to most knowledgeable sources on the subject, it is the most recent day (certainly that I can remember...) in which the year began on a Sunday with a full moon. Also day 1 was chosen as January 1, 4713 B.C. because the Julian Calendar, the Lunar Calendar and the Roman Tax Calendar all coincided. This happens every 7,980 years, so the next coincidence will be in 3267 A.D. I'll let you know if it actually happens that way next time...