The Calendars and Chronology 5 When the heliacal rising of Sirius was constituted the event which marked the beginning of the seasonal year, the reform was accompanied by the introduction of a calendar (the 'Sothic' calendar) whose opening day (i. I Sothic) always coincided with the heliacal rising: a 6th epagomenal day was intercalated as required, normally every 4th year, in order to maintain the relation . It was necessary to maintain a calendar which (more or less) kept step with the seasons for the purpose of fixing festival days (other than those of the New Moon and Full Moon festivals); for festivals were the occasions of the payment of tithes in kind to the temples. Before considering the scientific significance of the Sothic year and its calendar, it is desirable to go farther back in order to ascertain the calendric system and the 'year' which were superseded, officially at least, by the Sothic arrangement. The evidence is scanty, and consists mainly of the records of festivals shown as held at cyclic intervals of years on the Palermo Stone and the Cairo fragment;1 supplemented by an inscription from, the Edfu temple of about 200 B.C. which associates Imhotep with a revolt of the Set worshippers in Year 363 of an 'era of Horakhti' , In consequence the conclusions drawn from, this evidence must be regarded as conjectural. In the records down as far as the reign of Rameses II (1289- 1229) glimpses are obtained of a third calendar, in which I. X was coincident with I. I Sothic or on occasion with 2. I Sothic. Clearly then this calendar started each year with a day which was soon after the autumn equinox, and moving so as to keep about the same distance from it as I. I Sothic was from the summer solstice. Computation shows that such a calendar would result from 1 These are two fragments representing probably less than one-tenth of a tablet, possibly of three panels, of black diorite inscribed apparently during the period of the Fifth Dynasty -with records which purport to siiow the principal events of each regnal year since the accession of Menes.