Where the Month Names Come From: Gods, Emperors, and a Counting Error

Our modern month names originate from the ancient Roman calendar, deriving from Roman deities, agricultural rituals, political tributes to emperors, and Latin numbers. September through December still carry numbers from when the year began in March, creating a two-month offset after January and February were moved to the start.

Understanding where the month names come from reveals a centuries-long evolution driven by religious practice, political vanity, and astronomical corrections. What seems like a standardized twelve-part system is actually a composite archive of ancient Roman life, altered repeatedly by kings, senators, and emperors.

How a ten-month Roman calendar created a two-thousand-year counting error

The names of our final four months—September, October, November, and December—clearly state that they are the seventh, eighth, ninth, and tenth months. They derive directly from the Latin words septem (seven), octo (eight), novem (nine), and decem (ten). Yet in our modern calendar, they occupy the ninth, tenth, eleventh, and twelfth positions. This mismatch stems from an uncorrected shift in ancient Roman timekeeping.

According to historical tradition, Rome’s legendary founder Romulus established a ten-month calendar around 753 BCE. This calendar contained 304 days and began in spring with March (Martius). The uncounted winter period between December and March was simply ignored in the official calendar because no agricultural work or military campaigns took place during those cold months.

Around 713 BCE, King Numa Pompilius revised the system by adding two new months—Ianuarius (January) and Februarius (February)—to account for the winter gap, expanding the year to 355 days. Initially, these new months were placed at the end of the year or inserted into winter. However, in 153 BCE, the Roman Senate officially shifted the start of the civil year to January 1, the date when newly elected consuls took office.

When January and February became the first and second months of the year, the existing numbered months were pushed two places down the order. Quintilis (fifth) became the seventh month, Sextilis (sixth) became the eighth, September (seventh) became the ninth, and December (tenth) became the twelfth. Despite this major structural shift, the numerical names were never updated. This historical quirk caused a counting error that has persisted for over two millennia.

Which Roman gods and rituals gave us January through June?

The first six months of our year derive their names from Roman deities, religious ceremonies, or seasonal phenomena associated with spring and early summer.

January: Janus, god of gates and transitions

January honors Janus (Ianuarius), the Roman deity of doors, gateways, beginnings, and endings. Classical artists depicted Janus with two distinct faces: one looking backward into the past and the other looking forward into the future. This dual aspect made him the natural patron god for a month that oversees the transition from one calendar year to the next.

February: Februa, the rites of purification

Unlike the months named after specific gods, February takes its name from Februa, an ancient Roman festival of purification held mid-month. The term stems from the Latin verb februare, meaning to cleanse or purify. During the festival of Lupercalia on February 15, priests performed ritual cleansing ceremonies to purify the city and promote fertility for the upcoming spring season.

March: Mars, god of war and agriculture

March (Martius) was the original opening month of the early Roman calendar. It was dedicated to Mars, the god of war and the mythical father of Rome’s founders, Romulus and Remus. For ancient Romans, Mars was not only a military deity but also an agricultural guardian. March marked the arrival of warmer weather, signaling both the start of the farming season and the resumption of military campaigns after winter breaks.

April: Budding trees or the goddess of love

The exact origin of April (Aprilis) was debated even by Roman writers. The dominant theory links the name to the Latin verb aperire, which means “to open,” describing the unfolding of plant buds and flowers during mid-spring. Another widely accepted historical theory suggests Aprilis originally derived from Apru, an Etruscan borrowing of Aphrodite, the Greek goddess of love and beauty who corresponds to the Roman Venus.

May: Maia, goddess of growth and increase

May (Maius) is named after Maia, an ancient Roman earth goddess whose attributes centered on growth, fertility, and plant development. As the mother of Hermes (Mercury) in Roman myth, Maia represented the expanding warmth of late spring that allowed crops to flourish before the intense heat of summer arrived.

June: Juno, queen of the gods and protector of marriage

June (Iunius) honours Juno, the queen of the Roman pantheon, wife of Jupiter, and protector of women, marriage, and childbirth. Because Juno was believed to grant divine blessings to domestic unions formed during her sacred month, June became the traditionally favored month for weddings—a cultural preference that survives to this day.

How Julius Caesar and Augustus claimed July and August

The mid-year months of July and August originally carried plain numerical titles: Quintilis (“fifth month”) and Sextilis (“sixth month”). Their transformation into political memorials marked a permanent shift in how Roman leaders asserted their legacy.

In 44 BCE, following the assassination of Julius Caesar, the Roman Senate officially renamed Quintilis to Julius (July) in his honor. Caesar was born in that month and had overhauled the chaotic Roman timekeeping system two years earlier by establishing the solar Julian calendar in 45 BCE.

In 8 BCE, Caesar’s adoptive son and ultimate successor, Augustus Caesar, received a similar honor. The Senate renamed Sextilis to Augustus (August). Augustus specifically chose this month rather than his birth month (September) because several of his greatest military and political triumphs occurred during Sextilis, including the fall of Alexandria and his official consolidation of power over Egypt.

A persistent calendar myth claims that Augustus stole a day from February to make August 31 days long so his month would not be shorter than Julius Caesar’s July. Historical records from the period prove this story is false; Sextilis already had 31 days under the original Julian calendar reform introduced by Julius Caesar decades before the Senate renamed it for Augustus.

Why imperial ego failed to rename the rest of the year

Following the successful renaming of July and August, several later Roman emperors attempted to claim remaining months for themselves. However, none of these additions outlasted the rulers who ordered them.

Caligula briefly renamed September to Germanicus to honor his late father. Domitian later renamed September to Germanicus and October to Domitianus. Commodus took imperial vanity to its absolute limit: he ordered all twelve months to be renamed after his own official titles and epithets, transforming the calendar into Amazonius, Invictus, Felix, Pius, Lucius, Aelius, Aurelius, Commodus, Augustus, Herculeus, Romanus, and Exsuperatorius.

When these emperors died or were assassinated, the Roman public and Senate promptly abandoned the imperial renamings. The Senate frequently passed decrees of damnatio memoriae to erase tyrant legacies, reverting the calendar to its established divine and numerical names. Caesar and Augustus remained the sole exceptions because their renamings were tied to major, structural calendar overhauls and fundamental political shifts.

What were the months called before Roman influence spread?

Before Latin names took hold across Western Europe, native cultures used descriptive, environment-based calendars tied directly to farming, livestock management, and natural phenomena.

In 725 CE, the Anglo-Saxon monk Bede recorded the pre-Christian Old English month names in his treatise De temporum ratione. These names offer a window into an agrarian society where time was measured by practical survival tasks:

• May (Thrimilci): Meaning “three-milkings month,” named because grass growth was rich enough for cows to be milked three times daily.
• August (Weodmonath): Meaning “weed month,” referring to the rapid growth of wild vegetation during late summer.
• October (Winterfilleth): Meaning “winter full moon,” marking the official start of winter on the first full moon of the month.
• November (Blodmonath): Meaning “blood month,” designating the period when excess livestock were slaughtered and preserved for winter rations.

These descriptive names were eventually replaced by Roman month names as Latin Christianity and Roman literacy spread throughout Northern Europe during the Middle Ages.

How do non-Roman calendars name their months?

While the Roman system forms the baseline for civil timekeeping worldwide today, other major cultural calendars rely on distinct naming conventions:

The traditional Hebrew calendar uses month names adopted during the Babylonian exile in the 6th century BCE, such as Nisan, Tishrei, and Elul. Because the Hebrew calendar is lunisolar, it periodically adjusts to the solar year by inserting a full thirteenth intercalary month; see How the Hebrew Calendar Adds a Whole Leap Month to learn how this calculation works.

The Islamic calendar is purely lunar and consists of 12 months that shift backward through the solar seasons by roughly 11 days each year. Its month names originate from early Arabian environmental conditions; for example, Ramadan comes from the root word ramida, meaning intense, scorching heat.

East Asian systems historically relied on numeric designations rather than personal or mythological names. Traditional Chinese, Japanese, and Korean calendars numbered their months in sequence (First Month, Second Month, Third Month), eliminating political vanity and divine honorifics from timekeeping structure altogether.

Common calendar misconceptions and how the Gregorian reform fixed accuracy

A common error is confusing the establishment of month names with the creation of our current calendar system. Julius Caesar’s Julian calendar introduced a fixed 365-day year with a leap year every four years, creating an average year length of 365.25 days.

However, the actual solar year lasts roughly 365.2422 days. That tiny discrepancy of about 11 minutes per year accumulated over time, drifting by approximately one full day every 128 years. By the 16th century, the calendar had drifted 10 days out of sync with the natural astronomical equinoxes.

In 1582 CE, Pope Gregory XIII corrected this issue by introducing the Gregorian calendar. The reform dropped 10 excess days from October 1582 and refined the leap year rule: century years are not leap years unless they are evenly divisible by 400 (which is why 1600 and 2000 were leap years, but 1700, 1800, and 1900 were not). The Gregorian reform restored solar alignment while leaving the inherited Roman month names completely unchanged.

Understanding natural solar positions remains key to tracking shorter daylight shifts throughout the year; see Chasing Golden Hours: The Definitive Guide to Sunset in Houston, Texas for a concrete example of solar variance. Likewise, localized terms for short multi-week periods developed in parallel with full calendar months; see What Is a Fortnight? The 14-Day Word That Refuses to Fade to see how alternative time blocks persisted.

Frequently asked questions

Why do September, October, November, and December have numeric names that don’t match their position?

These months were originally the seventh, eighth, ninth, and tenth months of the ancient ten-month Roman calendar that started in March. When January and February were shifted to the start of the year in 153 BCE, these four months were pushed back two slots, but their original Latin numeric names were never changed.

Which month names are named after real historical people?

July and August are the only months named after real historical people. July was named in 44 BCE to honor Julius Caesar, and August was named in 8 BCE to honor Rome’s first emperor, Augustus Caesar.

Did Pope Gregory XIII change the month names when introducing the Gregorian calendar?

No, the Gregorian calendar reform of 1582 only corrected the leap year calculation and removed accumulated extra days to realign time with the solar equinoxes. Pope Gregory XIII retained all twelve traditional Roman month names.

Why did the early Roman calendar start in March instead of January?

The early Roman calendar was aligned with military campaigns and agricultural seasons, both of which resumed in spring after winter breaks. March was dedicated to Mars, the god of both war and agriculture, making it the natural choice to begin the active working year.