Februarius, fully Mensis Februarius ("month of Februa"), was the shortest month of the Roman calendar from which the Julian and Gregorian month of February derived. It was eventually placed second in order, preceded by "Ianuarius" ("month of Janus", January) and followed by "Martius" ("month of Mars", March). In the oldest Roman calendar, which the Romans believed to have been instituted by their legendary founder Romulus, March was the first month, and the calendar year had only ten months in all. "Ianuarius" and "Februarius" were supposed to have been added by Numa Pompilius, the second king of Rome, originally at the end of the year. It is unclear when the Romans reset the course of the year so that January and February came first.