Islam: A Guide for Jews and Christians - Electric Scotland

“ AND MUHAMMAD IS HIS MESSENGER” t 67
place, becomes clear only in the sequel. Muhammad began to send
his followers quietly and secretly in small groups to Yathrib. He
himself followed in September 622. This “migration,” or hijra, as
it was called in Arabic—Anglicized, from the Latin, as “hegira”—
though unmentioned in the Quran, was regarded by Muslims as a
turning point in the fortunes of the Prophet and his movement.
Note: According to report, it was the caliph Umar (r. 634–644 c.e.)
who chose the year 622 to mark the formal beginning of the Muslim
era, and documents began to be dated from it, counting, of course, by
lunar years of 354 days. The first year of the Muslim era—often denoted
in English as a.h. (Anno Hegirae) on the analogy with a.d.,
Anno Domini—was moreover dated back from 24 September, when
Muhammad actually migrated, to the first day of that lunar year, 16
July 622.