CALENDAR, JULIAN, the Roman adaptation of the Egyptian solar
calendar introduced by Julius Caesar, with the technical aid of
the Alexandrian astronomer Sosigenes, in 46 B.C.; that year was
extended to 445 days by intercalation in order to bring the
civic year into line with the solar year. While the Egyptians
divided the solar year of 365.25 days into 12 months of 30 days
each, with 5, or in every fourth year, 6, intercalary days added
after the last day of the twelfth month, the Romans, in their
Julian calendar, retained the 31 days of March, May, Quintilis
(July), and October, and the 28 days of February, as they had
been in the older Roman calendar, but increased the other
months, which until then all had 29 days, by one day (June,
April, September, November) or two days (January, Sextilis
[August], December), in order to have an annual total of 365
days. The intercalary month previously inserted periodically, at
the discretion of the pontifex maximus, after 23 February was
replaced by the intercalary day