The Coligny calendar: the Moon in the time of the Gauls

In November 1897, in a field near Coligny in the French department of Ain, more than a hundred bronze fragments came to light together with the remains of a statue. Reassembled, they turned out to be part of a large engraved tablet: a calendar in the Gaulish language, written in Latin characters. It is one of the longest texts we have in Gaulish and is kept in Lyon, in the museum devoted to the Roman city of Lugdunum. For the history of lunar calendars it is a unique witness.

A tablet of sixty-two months

The tablet, usually dated to the second century AD but carrying a system that is probably much older, presents a cycle of five years and sixty-two months: sixty ordinary months and two intercalary ones, inserted one at the start of the cycle and one halfway through. The months have thirty or twenty-nine days and are marked with the abbreviations MAT and ANM, usually interpreted as good and not good, or as complete and incomplete.

The twelve ordinary months appear on the tablet in abbreviated forms, including Samon, Duman, Riuros, Anagantio, Ogroni, Cutios, Giamoni, Simiuisonna, Equos, Elembiu, Edrini and Cantlos. Each month is divided into two halves of fifteen days, separated by the word ATENOVX, often translated as returning night or renewal, which may mark the passage from one lunar phase to another. Many days carry annotations that are still not fully understood.

What Caesar and Pliny said

Two Latin authors help to place the document. Caesar, in the sixth book of the Gallic War, writes that the Gauls measured time by counting nights rather than days, and that birthdays and the beginnings of months and years were reckoned with the night preceding the day. This is consistent with a lunar calendar, in which the month begins in the evening, when the Moon shows itself.

Pliny the Elder, in the sixteenth book of the Natural History, describing the gathering of mistletoe by the druids, states that they began their months, their years and a thirty-year cycle on the sixth day of the Moon. The report is brief and isolated, but it is the only explicit ancient testimony on the druids' lunar reckoning, and many scholars have compared it with the structure of the Coligny tablet.

The necessary caution

Many questions remain open. We do not know for certain whether the month began with the new Moon, the first quarter or the full moon, and scholars' proposals differ. The link between the month Samonios and the medieval Irish festival of Samhain, often taken for granted, is possible but not proven: the Irish sources are many centuries later and belong to another linguistic and cultural setting.

A second calendar of the same type, far more fragmentary, has been found at Villards-d'Héria in the French Jura, confirming that the Coligny calendar was not an isolated case. The fact that both were engraved in the Roman period, in Latin letters, suggests that the Gaulish system was still alive, perhaps in a religious setting, when Gaul had already been part of the empire for generations.

The Coligny calendar refutes the idea of Celts without astronomical knowledge, but it does not justify the fanciful reconstructions that have turned it into a druidic oracle. It is a technical document, the fruit of observations and corrections accumulated over time, showing a people engaged, like others, in reconciling the Moon with the Sun. Its real fascination lies precisely in this concreteness.