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
December (Roman month) "(VII Kal. Ian." on the pre-Julian calendar, when December had only 29 days). On the calendar of the Roman Republic and early Principate, each day was marked with a letter to denote its religiously lawful status. By the late 2nd century AD, extant calendars no longer show days marked with these letters, probably in part as a result of calendar reforms undertaken by Marcus Aurelius. Days were also marked with nundinal letters in cycles of "A B C D E F G H", to mark the "market week" December (Roman month) December (from Latin "decem", "ten") or mensis December was