On the ancient Roman calendar, mensis Februarius or Februarius ("February") was the second and shortest month, from which the English name of the month derives. It was preceded by Ianuarius ("January") and followed by Martius ("Mars' month", 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. Julius Caesar decided in 46 BC to move the start of the calendar from the beginning of March to the beginning of January.