Before 44 BC, the month of July was known as Quintilis, from the Latin "quintus" for fifth. It was renamed by the Roman consul Marcus Antonius in honor of Julius Caesar, who was born on July 15th. Also, in 8 BC the month of Sextilis was renamed in honor of Julius's successor, Augustus Caesar by the Roman Senate, even though Augustus was born in September. Sextilis is based on "sextus", Latin for sixth.

The next Caesar, Tiberius, put an end to the Senate's month renaming, with the remark, "And what will you do if there are thirteen Caesars?". Various other emperors, including Caligula and Domitian, attempted to rename the months, but they failed to last.