4.
The meaning of the passage is clear, and can be understood, as critics have already explained, only as implying the intercalation of a 366th day every fourth year. Some have asserted that Julius Caesar adopted this method of intercalating a day from the civil practice of the Alexandrines; others, on the contrary, appear disposed to believe that J. Caesar was the first to give an idea of it, according to the advice of Sosigenes. There is truth and error in both these opinions.
On the one hand, it is certain that Strabo, who visited Egypt a short time after the conquest of the country by the Romans, would not have omitted to attribute to them the institution of this year, if it really belonged to them. So far from doing so, he says (above, § 29) distinctly, that this method of intercalation was known and practised by the priests of Heliopolis and Thebes. Diodorus Siculus, who visited Egypt just at the time of the first arrival of the Romans, gives the same account as Strabo. Can we therefore believe that the Egyptians before this period were ignorant of the bissextile intercalation?
On the other hand; it is not less certain that this method of intercalation was only introduced into civil use at Alexandria from the time of Julius Caesar: before this period, the incomplete year of 365 days was adopted throughout the whole of Egypt, as is attested by a host of authorities, and confirmed by the date of the Rosetta stone, which only applies to this method of reckoning. Hence we see (I.) that Julius Caesar really obtained the idea of a fixed year of 365 1/4 days from the Egyptians, where it was employed for scientific or religious purposes only, whilst the incomplete year was the vulgar and common year; (II.) that he made this fixed year the common year, both among the Romans and Alexandrines, who were a people most readily disposed to adopt foreign innovations. It is, however, probable that the rest of Egypt preserved the ancient use of the incomplete year.