Quintilis was renamed July to honor Julius Caesar after his calendar reform.
Quintilis was the fifth month in the older Roman calendar, which began the year with March. After January and February were placed before it, Quintilis became the seventh month, but its traditional name remained. Following Julius Caesar’s assassination in 44 BCE, the Roman Senate renamed the month Julius, which became July in English.
Caesar’s calendar reform, introduced in 46 BCE and taking effect in 45 BCE, created the Julian calendar. It used a regular 365-day year with a leap day added every fourth year, correcting the drift of the earlier Roman system.
The next month, Sextilis, was later renamed August in honor of Augustus. July and August both have 31 days, a pattern sometimes explained by popular calendar myths rather than the actual history of the reforms.