During his time as dictator of the Roman Empire between the years of 49BC and 44BC, Julius Caesar ruled in an uncompromising and ruthless manner. And one change which Caesar ensured was implemented was the change of the calendar from the lunar cycle to the Julian calendar - which extended the year from 355 days to the current 365. Although the calendar was intended to correspond with the solar cycle, the extra quarter day forced Caesar to add an extra 24 hours - or leap day - every fourth year. This calendar remained the norm until the 16th Century when the Gregorian replaced the Julian in order to compensate for the fact Caesar's calendar did not take into account that a tropical year was in fact a few minutes shorter than 365-and-a-quarter days.