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) to December. Its length was increased to 31 days under the Julian calendar reform.