December (Roman month) December (Roman month) December (from Latin "decem", "ten") or mensis December was originally the tenth month of the Roman calendar, following November ("novem", "nine") and preceding Ianuarius. It had 29 days. When the calendar was reformed to create a 12-month year starting in Ianuarius, December became the twelfth month, but retained its name, as did the other numbered months from Quintilis (July) through December. Its length was increased to 31 days under the Julian calendar reform. The Romans did not number days of a month sequentially from the first day through the last. Instead, they counted back from the three
September (Roman month) holidays. Unless otherwise noted, the dating and observances on the following table are from H.H. Scullard, "Festivals and Ceremonies of the Roman Republic" (Cornell University Press, 1981), pp. 96–115. After the Ides, dates are given for the 30-day month of the Julian calendar; pre-Julian dates of festivals are noted parenthetically. September has a concentration of imperial birthdays "(dies natales)": Aurelian on the 9th, Trajan on the 18th, Antoninus Pius on the 19th, and Augustus on the 23rd. Inscriptions throughout the Empire record religious dedications made on these days, often by military personnel. The Genius of "Legio II Italica Pia", an