Coligny calendar

The Coligny calendar is a second century Celtic calendar found in 1897 in Coligny, France. It is a lunisolar calendar with a five-year cycle of 62 months. It has been used to reconstruct the ancient Celtic calendar. The letters on the calendar are Latin and the language is Gaulish.The calendar features "weeks" that consist of 5 days. Each month has six weeks and either 29 or 30 days. There are twelve such months in a year, totaling 354 days. A calendar cycle consisted of five years of this type, sixty regular months plus two intercalary months. For the calendar to remain in sync with the lunar phases, the five-year cycle must have been 1,831 days long. This would have made the calendar drift out of sync with the seasons by almost a day every year. Roman sources suggest that the Celtic calendar had a thirty-year cycle. The solar drift issue could have been dealt with by dropping a month once every 30 years. Each Celtic month started on the sixth day of the lunar cycle, according to Pliny the Elder. This is the date of the quarter moon, the easiest lunar date to confirm by direct observation.

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