Pre-Islamic Arabian calendar

The pre-Islamic Arabian Calendar was used by people in the Arabian Peninsula before the introduction of Islam. The calendar did not have a set length of days like our modern calendar, but instead had 354 or 355 days. It ran on a lunar cycle, which means it had 12 months and the months changed with the phases of the moon. Each month had either 29 or 30 days and it could take 33 or 34 years for the calendar to repeat itself. Because it didn't have a fixed length of days, it was often used to track religious festivals and other important dates rather than to mark exact dates on the calendar.