The Byzantine calendar is a historical calendar system used in the Byzantine Empire, which began in 5509 BC. It is based on the Julian calendar and counts years from the creation of the world, according to the calculations of early Christian scholars. The calendar consists of 12 months, with each month having either 30 or 31 days. In the Byzantine calendar, the new year traditionally started on September 1. This calendar was primarily used for religious purposes, including determining the dates of Christian feasts and events. Although it is no longer in common use, it played a significant role in the history of timekeeping in Eastern Orthodox Christianity.