The calendar of Romulus and Numa: the lunar origins of Roman time
The ten-month year credited to Romulus, Numa's reform with January and February, the month Mercedonius, the Fasti Antiates and Caesar's reform of 46 BC.
Latin authors tell that Rome's first calendar was the work of Romulus and had only ten months. It opened with Martius, dedicated to Mars, and closed with December, the tenth. The story must be taken with caution, because we know it from writers many centuries later, such as Censorinus and Macrobius. But the names of the months from September to December, meaning seventh, eighth, ninth and tenth, still preserve the trace of that ancient order.
The ten-month year
According to tradition, the year of Romulus lasted 304 days, divided into six months of thirty days and four of thirty-one: Martius, Maius, Quintilis and October were the long months. The winter period, between the end of December and the return of Martius, is said to have remained unnamed. Modern scholars debate whether this calendar ever existed in that form or is a learned reconstruction, but the idea of an uncounted winter is not considered impossible.
Ovid, in the Fasti, written at the beginning of the imperial age, voices the same tradition with an ironic line addressed to the founder: «you, Romulus, knew arms better than the stars». The quip reveals that the Romans of the Augustan age already looked on their first calendar as a rudimentary system, later corrected by a wiser king more attentive to the things of the sky.
Numa's reform
To the second king, Numa Pompilius, tradition credits the addition of Ianuarius and Februarius and a year of 355 days, very close to twelve lunar months. According to Macrobius, Numa chose odd lengths for the months, considered more favourable; only Februarius, the month of purifications and of the dead, had twenty-eight days. To keep pace with the Sun an intercalary month was periodically inserted, called Mercedonius or simply intercalaris.
Intercalation was managed by the pontiffs, who did not always apply it regularly. Ancient sources accuse them of lengthening or shortening the year to favour or harm magistrates and contractors. By the middle of the first century BC the calendar was so far out that, as Suetonius observes, the harvest festivals no longer fell in summer nor those of the vintage in autumn.
A painted calendar and the end of a system
The only Roman calendar earlier than Caesar's reform to have reached us is the Fasti Antiates Maiores, painted on plaster and found at Anzio in 1915. It dates to the first century BC and shows a year of 355 days with the intercalary month marked, the letters of the eight-day market cycle, called nundinal, and the abbreviations that distinguished the fasti days, on which public business could be conducted, from the nefasti.
In 46 BC Julius Caesar, with the help of the Alexandrian astronomer Sosigenes according to Pliny the Elder, put an end to the system. To realign the calendar that year lasted 445 days, and Macrobius remembers it as the last year of confusion. From 45 BC Rome adopted a solar year of 365 days with an extra day every four years, and the link between months and Moon was broken for good.
And yet the Moon did not vanish entirely from the Roman calendar. The Kalends, Nones and Ides, the three reference days by which the Romans dated every month, were originally tied to the phases of the Moon, and they remained in use for centuries, into the Middle Ages and beyond. In the civil time of the West there thus survives a framework born to follow the Moon.