R. Naḥshon Gaon: Calendar Scholar or a Pseudo-Author?

R. Naḥshon ben Zadok, gaon of the Academy of Sura from 874 to 882, is best known for his many responsa, and is credited with developing a system of calendation known as ʿIggul de-Rav Naḥshon Gaon. This system assumes that the Jewish calendar recurs every 247 years and, unlike the normative Rabbinic calendar, does not depend on calculation. Due to its simplicity ʿIggul de-Rav Naḥshon Gaon was very popular in the Middle Ages and early modern period. However, the ʿIggul is incompatible with the standard Rabbinic calendar, so that following it can lead to celebrating important religious holidays, such as Passover and the Day of Atonement, at wrong times. This problem was often discussed by medieval and early modern authors who attempted to explain why a gaon, the highest halakhic authority, had advocated a non-standard and deviant calendar.
This paper looks at the association of R. Naḥshon gaon with the Jewish calendar in general and with the ʿIggul de-Rav Naḥshon Gaon in particular. Drawing on manuscript evidence it argues that the attribution of the reiterative calendar to R. Naḥshon gaon is anachronistic and mainly restricted to Ashkenaz. The paper also tries to understand why R. Naḥshon gaon was chosen as a pseudo-author of the reiterative calendar.