Roman calendar
The Roman calendar began as a ten-month system credited to the legendary first king Romulus. This early year started in March and ended with December, leaving winter as an unassigned span of days before the next cycle. Each month held either 30 or 31 days, creating a total of 304 days for the entire year. These months ran for exactly 38 nundinal cycles, which functioned as an eight-day week counted inclusively by Romans. The system included religious rituals and public markets at the end of each cycle. Modern historians dispute whether this calendar was truly lunar or simply agricultural. Some scholars argue it tracked seasonal markers like leafing trees and animal migration rather than moon phases. Others suggest it reflected Pythagorean influences from Southern Italian Greeks during the kingdom era. Plutarch recorded alternative traditions where the year lasted 360 days with haphazardly assigned month lengths. Censorinus claimed Romulus borrowed the system from Alba Longa, his supposed birthplace. Late Republican writers often attributed these origins to Romulus despite lacking contemporary evidence.
Numa Pompilius, the second king of Rome, divided the year into twelve lunar months according to Livy's account. He added fifty days to the calendar while removing one day from each thirty-day month to create January and February. This resulted in a lunar year of 354 days that fell short of the solar year by about eleven days annually. To correct this mismatch, Roman priests inserted an intercalary month called Mercedonius between February 23 and 24. In common years the calendar held 355 days, while leap years reached 377 or 378 days depending on the length of Mercedonius. The Pontifex Maximus determined when to insert these extra days based on political needs rather than astronomical accuracy. Varro noted that the twelfth month was February, and when intercalations occurred, the five last days were removed. Macrobius described how Romans placed the intercalary month after February 23 to avoid nones falling on market days. By 170 BC, Intercalaris began on the second day after February 23, and in 167 BC it started immediately following that date. The system eventually broke down during the Second Punic War, leading to reforms like the 191 BC Acilian Law.
Control over intercalation became a tool for political gain among Roman magistrates during the late Republic era. The position of Pontifex Maximus was not a full-time job but held by elite members involved in daily politics. A Pontifex had incentive to lengthen years when allies held power or shorten them when opponents governed. Julius Caesar exploited this authority as pontifex maximus after winning his civil war. He reformed the calendar in 46 BC, making his third consulship year last 446 days instead of the usual 355. This extended year included three intercalary months inserted before December kalends. Livy recorded astronomical events showing the civil calendar varied from the solar year by an entire season by 190 BC. By 168 BC, the calendar remained two months off alignment with actual seasons. Cicero's speeches and letters provide established chronology back to about 58 BC through these manipulations. The breakdown occurred again in the middle of the first century BC due to increasingly chaotic Roman politics. Priests manipulated dates to serve their own interests rather than maintain seasonal accuracy.
Julius Caesar ordered a complete reformation of the calendar in 46 BC following his victory in civil war. Scholars including Alexandrian Sosigenes and Roman M. Flavius designed the new Julian calendar as entirely solar. They distributed ten additional days throughout existing months without adjusting nones or ides. The reform created a single leap day every fourth year by repeating February 24, known as bissextile. After Caesar's assassination, priests mistakenly added the leap day every three years due to inclusive counting methods. Augustus suspended intercalation for one or two decades to restore proper calendar position. In 8 BC, plebiscite Lex Pacuvia de Mense Augusto renamed Sextilis August in his honor. The Julian calendar measured 365.25 days per year, slightly longer than the tropical year of 365.24 days. By the 16th century, Easter had shifted so far from vernal equinox that Pope Gregory XIII ordered further corrections. This resulted in establishing the modern Gregorian calendar method. Augustus's birthday on September 23rd became ambiguous under the new system, causing honorary festivals to be held on either date.
Years began to be dated by consulships after the establishment of the Republic in 509 BC. Ordinary consuls were elected annually, though temporary and honorary ones existed but were not used for dating. Consular lists appeared on public calendars displayed throughout Rome. The traditional list of Roman consuls served as the primary dating method until AD 541 when nonimperial consuls ceased appointment. Diocletian began 15-year indiction cycles starting from the AD 297 census, which became required format under Justinian. Constantine formally established the 7-day week by making Sunday an official holiday in AD 321. Some provinces maintained local eras; Africa dated records sequentially from 39 BC while Spain started from AD 38. Varro calculated the founding of Rome at 753 BC, though other writers varied by several decades. Such ab urbe condita dating never achieved widespread adoption across the empire. After consuls waned in importance, most Roman dating shifted toward regnal years based on emperors' terms. The Orthodox subjects of Byzantine Empire used Christian eras including those based on Christ's incarnation or world age. These cycles remained undistinguished so that year two of indiction could refer to any of multiple possible dates.
Historians have reconstructed correspondence between Roman dates and Julian equivalents using disparate ancient sources. Detailed accounts exist of decades leading up to the Julian reform through Cicero's speeches and letters permitting chronology back to about 58 BC. Astronomical events recorded by Livy show calendar misalignment: a solar eclipse occurred on 11 Quintilis but actually happened on the 14th of March 190 BC in proleptic Julian calendar. A lunar eclipse noted before Battle of Pydna dated as the 3rd of September actually occurred on the 21st of June 168 BC. These discrepancies mean verified dates are invariably weeks to months outside their proper place. Nundinal cycle and known synchronisms generate contested chronologies back to start of First Punic War in 264 BC. Beyond that point, dates remain roughly known based on harvest dates and seasonal religious festivals. Chris Bennett created reconstructions of early Roman dates in terms of Julian calendar available online. Uncertainty regarding end of lunar dating and irregular intercalation means modern historians must rely on clues like festival timing rather than precise records. The continuity of names from Roman to Gregorian calendars often leads mistaken belief that they correspond directly without adjustment.
Continue Browsing
Common questions
Who created the original Roman calendar system?
The legendary first king Romulus credited with creating the early ten-month Roman calendar. This initial system started in March and ended with December, leaving winter as an unassigned span of days before the next cycle.
When did Numa Pompilius add January and February to the Roman calendar?
Numa Pompilius divided the year into twelve lunar months during his reign as the second king of Rome. He added fifty days to the calendar while removing one day from each thirty-day month to create January and February.
What date was Julius Caesar's calendar reform enacted in 46 BC?
Julius Caesar ordered a complete reformation of the calendar in 46 BC following his victory in civil war. The new Julian calendar measured 365.25 days per year by distributing ten additional days throughout existing months without adjusting nones or ides.
How many days were in the earliest Roman calendar year under Romulus?
Each month held either 30 or 31 days, creating a total of 304 days for the entire year. These months ran for exactly 38 nundinal cycles which functioned as an eight-day week counted inclusively by Romans.
Why did the Roman calendar break down during the Second Punic War?
Control over intercalation became a tool for political gain among Roman magistrates during the late Republic era. Priests manipulated dates to serve their own interests rather than maintain seasonal accuracy, leading to reforms like the 191 BC Acilian Law.