The Coligny calendar is a peg calendar (or parapegma) made in Roman Gaul in ca. the 2nd century AD, giving a five-year cycle of a lunisolar calendar with intercalary months. It is the most important evidence for the reconstruction of an ancient Celtic calendar. It is written in Latin inscriptional capitals and is in the Gaulish language. The restored tablet contains sixteen vertical columns, with 62 months distributed over five years.
It was found in Coligny, Ain, France (WikiMiniAtlas 46°23′N 5°21′E / 46.383°N 5.350°E / 46.383; 5.350) near Lyon in 1897, along with the head of a bronze statue of a youthful male figure. It is a lunisolar calendar. It is now held at the Gallo-Roman Museum of Lyon-Fourvière.
It was engraved on a bronze tablet, preserved in 73 fragments, that originally was 1.48 m wide and 0.9 m high (Lambert p. 111) or approximately 5 feet (1.5 m) wide by 3½ feet in height. Based on the style of lettering and the accompanying objects, it probably dates to the end of the 2nd century AD. It is written in Latin inscriptional capitals and is in the Gaulish language (Duval & Pinault). The restored tablet contains sixteen vertical columns, with 62 months distributed over five years.
The French archaeologist, J. Monard, speculated that it was recorded by druids wishing to preserve their tradition of timekeeping in a time when the Julian calendar was being imposed throughout the Roman Empire. However, the general form of the calendar suggests the public peg calendars (or parapegmata) found throughout the Greek and Roman world (Lehoux pp. 63–65).
A similar calendar found nearby at Villards d'Heria ( WikiMiniAtlas 46°25′N 5°44′E / 46.417°N 5.733°E / 46.417; 5.733) is only preserved in eight small fragments. It is now preserved in the Musée d'Archéologie du Jura at Lons-le-Saunier.
More information on the Wikipedia page [1].. Tehre is various other coverage, eg [2].