 This intercalary month was formed by inserting 22 or 23 days after the first 23 days of February; the last five days of February, which counted down toward the start of March, became the last five days of Intercalaris.The net effect was to add 22 or 23 days to the year, forming an intercalary year of 377 or 378 days.Some say the "mensis intercalaris" always had 27 days and began on either the first or the second day after the Terminalia (23 February).