Origins
July is Caesar's month, the first month in human history to bear the name of a mortal rather than a deity. Its renaming in 44 BCE — the year of Caesar's assassination — inaugurated a tradition of calendrical self-glorification that would be imitated by emperors, revolutionaries, and dictators for the next two millennia.
The month was originally called 'Quīntīlis' in Latin, meaning simply 'the fifth' (from 'quīntus'), because it was the fifth month in the ten-month calendar of Romulus, which began in March. The name Quīntīlis persisted for over six centuries, through the entire Roman Republic, until the month was renamed 'Iūlius' in 44 BCE, shortly after the assassination of Gaius Julius Caesar on the Ides of March (March 15) that same year.
The renaming was proposed by Mark Antony (Marcus Antonius), Caesar's fellow consul and political ally, and ratified by the Roman Senate. The choice of Quīntīlis for the honor was based on the fact that Caesar was born in this month — traditionally on July 12 or 13, around 100 BCE. The act was simultaneously a political tribute, a demonstration of the power of the Julian faction, and a precedent that would soon be followed when Sextīlis was renamed Augustus for Caesar's adopted heir.
Development
The name 'Iūlius' derives from the 'gens Iulia,' the Julian clan, one of the oldest and most prestigious patrician families in Rome. The Iulii claimed descent from Iulus (also called Ascanius), the son of the Trojan hero Aeneas, and through Aeneas from Venus herself. This divine genealogy was politically useful — Caesar exploited it ruthlessly — and it meant that naming a month 'Iūlius' was, in a sense, also a dedication to Venus, blurring the line between honoring a man and honoring a goddess.
Caesar's connection to the calendar extends far beyond the month that bears his name. In 46 BCE, acting on the advice of the Alexandrian astronomer Sosigenes, Caesar reformed the entire Roman calendar, replacing the chaotic and politically manipulated Republican calendar with a solar calendar of 365 days and a leap day every four years. This 'Julian calendar' was a masterpiece of practical astronomy that remained the standard calendar of the Western world for 1,627 years, until Pope Gregory XIII's reform of 1582 corrected the Julian calendar's slight overestimation of the solar year (365.25 days versus the actual 365.2422 days).
The English word 'July' entered the language from Anglo-Norman 'Julie,' itself from Latin 'Iūlius.' The Anglo-Saxons called this month 'æfterra līða' (later mild-month) or 'hēafodmōnaþ' (hay-month). The Italian form 'luglio' is noteworthy for its unusual phonological development from Latin 'Iūlius' — the initial 'l' is thought to result from dissimilation or contamination with another word.
Modern Usage
July's pronunciation in English deserves comment. Modern English stresses the second syllable (/dʒuˈlaɪ/), but earlier English stressed the first, and the pronunciation /ˈdʒuː.laɪ/ persisted in dialectal and poetic usage through the nineteenth century. Shakespeare's plays scan 'July' with first-syllable stress.
The political precedent set by July's renaming proved irresistible. Augustus followed in 8 BCE (or possibly 8 CE) with the renaming of Sextīlis to Augustus. The emperor Nero renamed April 'Neroneus,' Claudius renamed March 'Claudius,' Domitian renamed September and October after himself — but none of these later renamings survived their sponsor's reign. Only Julius and Augustus achieved permanent calendrical immortality, their names spoken billions of times daily across every language that inherited the Roman calendar.
In the modern world, July's cultural significance is dominated by national celebrations: July 4 (American Independence Day), July 14 (Bastille Day in France), and July 1 (Canada Day). None of these have any connection to Julius Caesar, yet they ensure that his name is shouted, sung, and printed on countless banners and invitations every year — a form of immortality that even Caesar himself might not have imagined when Mark Antony proposed the renaming in the shocked and turbulent weeks after the Ides of March.