Bissextile, Or Leap-Year. An intercalary day was thrown into every fourth year to adjust the calendar, and make it agree with the sun's course. It originated with Julius Caesar, who ordered a day to be counted before the 24th of February, which among the Romans was the sixth of the calends, and which was therefore reckoned twice, and called bissextile : this added day we name the 29th of February every fourth year, forty-five years B.C.