The Roman Calendar: Twelve Months of Politics
The calendar you use today is a Roman calendar. The twelve months, the seven-day week borrowed from Near Eastern sources and transmitted through Rome, the numbering of the years from a fixed point that eventually became the Christian era — all of these are features of the system that Julius Caesar reformed in 46 BC and that the Catholic Church adjusted in 1582 with modifications so minor that most countries now use what is, in its essentials, the calendar Caesar commissioned. You wake up on a Tuesday in October because a Roman dictator in the first century BC decided to align the civil year with the solar year, and his solution was good enough to last two thousand years.
The Roman calendar before Caesar was a mess. The original Republican calendar had 355 days organized into twelve months, which meant it fell steadily behind the solar year — roughly eleven days per year — so that the months progressively drifted out of alignment with the seasons. The solution was supposed to be the addition of an intercalary month — Mercedonius, inserted every two or three years — that would keep the calendar roughly synchronized with the solar cycle. In practice, the pontiffs who controlled the intercalation used this power for political purposes: extending magistracies, delaying elections, manipulating the timing of public festivals and business days. By Caesar’s time the calendar was so far out of alignment that the summer months were falling in autumn.
Caesar’s reform, implemented with the advice of the Alexandrian astronomer Sosigenes, replaced the lunar month system with a solar calendar of 365 days with an intercalary day inserted every four years — the leap year. The 365.25-day year approximated the actual solar year closely enough to maintain calendar alignment over centuries, though not quite perfectly — the actual solar year is 365.2422 days, a difference of about 11 minutes per year that accumulated to roughly ten days by the sixteenth century, requiring the Gregorian reform that dropped certain leap years to bring the calendar back into astronomical alignment. The Julian calendar was in use for sixteen centuries before this adjustment was needed, which is a reasonable measure of its accuracy.
The transition from the old calendar to the new in 46 BC required an extraordinary one-time correction: the year had to be extended by 67 days — two intercalary periods — to bring the calendar back into alignment with the solar year. Ancient sources call 46 BC the Year of Confusion, which understates the situation: the year lasted 445 days. Caesar had the authority to impose this correction because he held the dictatorship, and nobody was in a position to dispute the change even if they found its practical implications disorienting.
The months of the Julian calendar retained the names that had accumulated through Roman religious and political history, some of which were already old by Caesar’s time. January came from Janus, the two-faced god of beginnings and passages. February came from the februa, purification rites held late in the old year. March came from Mars. April’s etymology is disputed — possibly from Aphrodite, possibly from aperire, to open, as in the spring’s opening. May and June are named for Maia and Juno. July was renamed in Caesar’s honor — it had been Quintilis, the fifth month in the original calendar’s numbering — and August was renamed for Augustus, transforming what had been Sextilis. September, October, November, and December retain their numerical names from the ten-month calendar — seventh, eighth, ninth, tenth — that predated the addition of January and February, which is why they no longer match their positions in the twelve-month year.
The seven-day week was not Caesar’s innovation and was not originally Roman. It came from the Babylonian tradition of associating days with celestial bodies — the seven known planets: the Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn — and entered the Roman calendar through astrological practice in the first century AD, spreading across the empire along with astrology and the Near Eastern religious traditions that had adopted it. The planetary names survive in the weekday names of the Romance and Germanic languages: Saturday is Saturn’s day, Sunday the Sun’s day, Monday the Moon’s day, and the others carry their planetary names in either Latin or Germanic equivalents depending on the language. The week was not officially incorporated into the Roman civic calendar until Constantine in the early fourth century.
The practical consequence of the Julian calendar’s durability is that the basic temporal framework within which all of recorded Western history is organized is a Roman political artifact. The months that historians use to date the Fall of Rome, the Black Death, the French Revolution, the Second World War are the months that Caesar created. The leap years that correct the calendar’s drift are Caesar’s invention. The week whose rhythm structures modern working life is a Roman adoption of a Babylonian astrological system. The modern world keeps time by Roman clocks, which is perhaps the most complete form of Roman legacy there is: not stone and concrete but the invisible framework within which everyone organizes their days.