Calendars in pre-Islamic Arabia

Pre-Islamic Arabia was a home to many calendars, mostly known from inscriptions. Calendars often varied by region, and cities or kingdoms often used a lunar calendar, a lunisolar calendar, and much more rarely, a solar calendar. Lunisolar calendars used the lunar phases of the moon to count months and the rotation of the earth around the sun to count years. Because twelve lunar months are 11–12 days shorter than a solar year, lunisolar calendars used intercalation to synchronize the months with the seasons and years.

Across Arabia, three main calendrical traditions have been discovered: the northern Arabian tradition, the tradition of the Najran oasis, and that of South Arabia more broadly. Inscriptions of the ancient South Arabian calendars reveal the use of a number of local calendars, as do Safaitic inscriptions from the Harran desert in Syria and Jordan. At least some of the South Arabian calendars followed the lunisolar system, while the Safaitic calendar had fixed months and seasons and, very importantly, a seasonal star calendar strongly connected to the Zodiac and the position of the ʔanwāʔ. The ʔanwāʔ, a series of asterisms on or near the zodiac belt were the most important element in pre-Islamic astronomy. These stars were connected to the season, and they were used to forecast various phenomena such as rain, temperature, wind.

After the Roman conquest of the Nabataean Kingdom, the newly created province of Arabia Petraea kept its old calendar, but began counting years according to the Era Provincia Arabia, or the Bostran era, which begins in 106 AD (the date of the conquest). This was an unusual combination, since the north Arabia used a lunar calendar system, while the Romans used a solar calendar system, though this combination is not unattested.

Little epigraphic evidence exists for the Meccan calendar outside of Abbasid-era Muslim tradition. Some historians maintain that it was a purely lunar calendar, similar to the modern Islamic calendar, whereas others believe that this was true only until the two centuries before the Hijra, when it became a lunisolar calendar with an intercalary month.