Since the year 45 B.C., Julius Caesar introduced, in the whole Roman
world, the Egyptian calendar with 365 days and six hours i.e. 365, 25, adding the necessary
days in the shorter months. It was also intercalated one day between the 23rd and the
24th of February every four years, which was called bissextile because the 6th day before
the calends of March counted twice. This day gave the name to the year where it was
included but it was not the 29th of February, which did not exist at the time. This calendar
became known as the Julian calendar and lasted until the 1st of January 1582 when
Pope Gregory VIII made its last modification, implementing what we know as Gregorian
calendar, which has been in use till the present day. The adopted Egyptian calendar had
a mathematical simplicity; it didn’t require any adjustments by means of intercalary days
or months and was used to date every official or officious act, thus justifying Julius Caesar’s
statement: «the only intelligent calendar of Mankind’s history». He had for advisor
an Egyptian hemerologist, the astronomer Sosigenes from Alexandria, an Egyptian about
whom we know little but who managed to impose his ideas about this issue to Julius Caesar
not only because they were good but also because they were based on a millennial
practice.