This article exposes an analysis of the Zoroastrian Persian calendar in a 12th century Hebrew book on the Jewish calendar (Sefer ha-‘Ibbūr). The Hebrew treatise was composed by the polymath Abraham bar Ḥiyya, probably in Northern France. Bar Ḥiyya depicts the structure of the Zoroastrian Persian calendar, its months and some of its festivals. He then expounds on calendrical algorithms which enable to convert between Persian and Jewish dates. Although one finds the names of some Persian months and festivals in earlier Jewish sources, Abraham bar Ḥiyya’s text not only elaborates in greater detail on these matters, but for the first time in Hebrew literature, one encounters conversion algorithms between the two calendars.
