Today is Jan. 1, 2763, on the old Julian calendar. The years were originally counted from the founding of the city of Rome. The system was seriously flawed, however, and slowly got out of sync with the seasons. So it was replaced, beginning in 1582, with the Gregorian calendar we use today. Its leap-year rules were devised to solve the calendar creep problem. The Julian system, meanwhile, continues to fall behind. Jan. 1 (Julian) will slip to Jan. 15 (Gregorian) in 2101.