February was named after the Latin term februum, which means purification, via the purification ritual Februa held on February 15 in the old Roman calendar. January and February were the last two months to be added to the Roman calendar, since the Romans originally considered winter a monthless period. They were added by Numa Pompilius about 700 BCE. February remained the last month of the calendar year until the time of the decemvirs (c. 450 BCE), when it became the second month. At certain intervals February was truncated to 23 or 24 days and a 27-day intercalary month, Intercalaris, was inserted immediately after February to realign the year with the seasons.
Under the reforms that instituted the Julian calendar, Intercalaris was abolished, leap years occurred regularly every fourth year (after a few years of confusion), and in leap years February gained a 29th day. Thereafter, it remained the second month of the calendar year, meaning the order that months are displayed (January, February, March, , December) within a year-at-a-glance calendar.