This month was supposed to be inserted every two or three years to align the 355-day common year with the tropical year. The decision whether to insert the intercalary month was made by the pontifex maximus, supposedly based on observations to ensure the best possible correspondence with the seasons. Unfortunately the pontifex maximus (whose office was generally held by a politician or soldier, notably Julius Caesar during the so-called Years of Confusion) often neglected to insert the month at the proper time, or deliberately inserted it early or late to allow some officials to stay in office longer or force others out early. Such unpredictable intercalation meant that dates following Februarius could not be known in advance; neither could the current date for citizens out of communication with the city.
The month was eliminated by Julius Caesar when he introduced the Julian calendar in 46 BC.