Difficulty arises as one tries to combine the lunar cycles with the solar year. In fact, the average Moon year of twelve months is of 354. 3669 days compared to the average 365. 2422 days of the solar cycle.
The task was to combine these two years into one synchronous year and still keeping tract with seasonal changes. The solution was found in the intercalary 6 month and year, which introduces every third year a thirteenth month called Santarana. This technique of inserting an extra month is qualified as embolistic for clotting or leap month. Apart from the use of an additional leap month there was the possibly of adding an extra day in July thus complicating things further. The first leap month was called Ciallobuis Sonnocingos which means, check-up of the Sun's course, returns every five years and the second, Mens in Dueixtionu, inserted between October and November also runs every five years at the beginning of each lustrum. Mens in Dueixtionu means month in duplication and is found abridged as MIDX in the Coligny Calendar.
THE COLIGNY CALENDAR
Month Name Number of days Code
SAMONIOS 15 + 15 = 30 mata (even)
DUMANNIOS 15 + 14 = 29 anmata (not even)
RIUROS 15 + 15 = 30 mat
ANAGANTIOS 15 + 14 = 29 anm
OGRONIOS 15 + 15 = 30 mat
CUTIOS 15 + 15 = 30 mat
GIAMONIOS 15 + 14 = 29 anm 7
SIMIUISONIOS 15 + 15 = 30 mat
EQUOS 15 + 14 = 29 anm or 15 + 15 = 30
ELEMBIUOS 15 + 14 = 29 anm
EDRINIOS 15 + 15 = 30 mat
CANTLOS 15 + 14 = 29 Anm
Source: The Calendar and Almonach of the Ancient Druids By Michel-Gérald Boutet, 2001
Image: The Caligny Calendar