Beginning of the Islamic Calendar

In 622 Muhammad and his followers left Mecca for Yathrib, the city later called Medina. That migration, the Hijra, was a journey over days, not a single dated instant. It gave the new community a home and a political footing, and its year became the reference point of the Islamic era.

The calendar itself was adopted about sixteen years later, under the caliph Umar. Counsellors chose the year of the Hijra as its starting point and kept Muharram as the first month. The epoch, 1 Muharram, is a calculated date, conventionally 16 July 622 in the Julian calendar, and not the day the travelers entered Medina.