In the early days when the Babylonians began to invent the calendar. Moon is based in the count at the end of 12 months to 1 year, and to achieve a balance between the calendar year with the seasonal year. We've added a month for 1 month to 13 months in every four years later, the Egyptians, Greek and Semitic c. Have led to modify the calendar of the Babylonians. Of King Juliet Caesar introduced the idea of an astronomer Egyptian name on Beziers Nice to be modified one year with 365 days every four years to fill a month with 28 days up to 1 day to 29. is called leap day in February 2125 on Equinox in March to be held on March 11 instead of March 21. So Pope Gregory the 13th, so adjusted deduction to 10 days. the calendar And the day after October 4, 2125 instead of October 5 was changed to October 15, the new calendar is called. Gregorian calendar Arion Adopted January 1 as the beginning of the year.