In 45 BC, Julius Caesar instituted a new calendar (the Julian calendar) that corrected astronomical discrepancies in the old.
Romulus vanished in the 54th year of his life, on the Nones of Quintilis (July), on a day when the Sun was darkened.
Julius (July) was renamed from Quintilis ("fifth" month) in honor of Julius Caesar, who had adopted his grand-nephew Octavian, the future Augustus, and made him his heir.