Every four years, an extra day is added to the calendar, But even with leap day, the math doesn't exactly, well, math.

Caesar's reform plan called for a fixed, 12-month, 365-day calendar beginning with the first of January and ending with the last day of December. In earlier times (as previously noted), Romans had ...

Eventually, during Julius Caesar's rule, the calendar no longer matched the actual seasons so the emperor adopted a 365-day calendar and added 10 days the calendar, including a leap day in ...