The first day of the Islamic calendar, Muharram 1, A. Their language belonged to the Nahuatlan subfamily of Uto-Aztecan languages. Present-day calendars include the Gregorian calendar, which is in use throughout most of the world, and the Moslem, Jewish, and Chinese calendars.
The chief trouble with this system was that in a four-year cycle there were four days too many. The church calendar with its movable feasts shows an interesting example of a harmony of several different systems.
Similarly four years of about 365 1-4 days each can be approximated by taking three years of 365 days and a fourth year of 366.
This fourth year with its intercalary day is the leap year.
If calculations are by the lunar cycle, the surplus of the solar over the lunar year (365 over 354) can be somewhat rectified by adding an intercalary month of 33 days every three years.
Reckoning of day and year was considered necessary by many ancient peoples to determine sacred days, to arrange plans for the future, and to keep some intelligible record of the past.