When were January and February added to the calendar?

The addition of January and February to the Roman calendar is attributed to King Numa Pompilius, the second king of Rome, who reigned from 715 to 673 BCE. According to Roman tradition, Numa added these two months around 713 or 712 BCE to align the calendar with the lunar year, which was the basis of the Roman calendar at that time.

The original Roman calendar, believed to have been established by Romulus, the legendary founder of Rome, started with March as the first month. The months of January and February were inserted between December and March during Numa’s reign to bring the total number of months to 12. This adjustment helped synchronize the calendar with the lunar phases and agricultural seasons.