Wikipedia
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.
Februarius was the only month in the pre- Julian calendar to have an even number of days, numbering 28. Ancient sources derived Februarius from februum, a thing used for ritual purification. Most of the observances in this month concerned the dead or closure, reflecting the month's original position at the end of the year. The Parentalia was a nine-day festival honoring the ancestors and propitiating the dead, while the Terminalia was a set of rituals pertaining to boundary stones that was probably also felt to reinforce the boundary of the year.