The main source mentioning the last intercalation in the Sasanian times is Bērōnī’s accounts in his early work on the chronology of ancient nations, the Vestiges of the Past Centuries, and also in his later masterpiece consisting of an encyclopedia of astronomical sciences, the Canon Masudicus. However under the pretext that there is a contradiction in Bērōnī’s accounts as he has given two different “dates” for the same alleged intercalation, i.e. in the reign of Yazdegird I and in that of Pērōz, the historical existence of the intercalary cycle in the Persian calendric system has been thoroughly discredited. It is surprising to see the non-attentive reading of Bērōnī’s accounts of the intercalation of the Persian calendar in its history; and, moreover, if we review most of the modern authors on the subject, their lack of familiarity with both the Perso-Aryan vision and the elements of Persian calendars is astounding.
In his Chronology, Bērōnī draws forth his account from the Mazdayasnian books which treat of the calendar of Persian festivals, and also from the set of astronomical tables of the Persian astronomers, the Zīg ī Šahriyārān; his account is not a mere translation of Persian texts, but it is often accompanied by a commentary that could be used as a basis for a mathematical assessment. In his Canon, Bērōnī summarizes his previous account while correcting some minor errors.
The present article deals with the question of the last intercalation made by Persian astronomers as described by Bērōnī.
