Establishment of the Islamic Hijri Calendar

In 638 CE, Caliph Umar ibn al-Khattab established the Islamic lunar calendar as the official dating system for the Muslim empire. The calendar's starting point was set to Prophet Muhammad's migration from Mecca to Medina in 622 CE, beginning with the month of Muharram. The first day corresponds to July 16, 622 CE on the Julian calendar. This system became the standard for Islamic religious observances and administrative functions, and continues to determine Islamic holidays and rituals today.