Coligny calendar


The Coligny calendar is a bronze plaque with an inscribed calendar, made in Roman Gaul in the 2nd century CE. It lays out a 5-year cycle of a lunisolar calendar, each year with 12 lunar months. An intercalary month is inserted before each 2.5 years. It is the most important piece of evidence enabling the reconstruction of an ancient Celtic calendar.
The calendar was found in 1897 in France, in Coligny, Ain, along with broken pieces of a life-size bronze statue of a nude male holding a spear, likely meant to portray Mars, the Roman god of war. Approximately 40% of the original calendar remains in the form of fragments. It was engraved on a bronze tablet, preserved in 73 fragments, that was originally 134.8 cm wide by 78.0 cm high. With the rim attached the plate measured 52 by 32 unciae Drusianae. It is written in the Gaulish language with the Latin alphabet, using Roman square capitals and Roman numerals. Based on the style of lettering and the accompanying statue, the bronze plaque likely dates to the end of the second century CE, although copying errors indicate that the calendar itself is much older. It is now held at the Gallo-Roman Museum of Lyon-Fourvière.
Eight small fragments of a similar calendar were found at the double-shrine of Villards-d'Héria. It does not have the holes of a peg calendar that the Coligny calendar does, but otherwise has the same notations. It is now held in the at Lons-le-Saunier.

List of months

The names of the twelve lunar year months are reconstructed as Samonios, Dumannios, Rivros, Anagantios, Ogronios, Cutios, Giamonios, Simivisonnios, Equos, Elembivios, Edrinios, and Cantlos. The names occur in the genitive form SAMONI, DUMANNI, RIVRI, etc. in the internal notations of the calendar. The name of the first intercalary month may be listed at the end of the month as QUIMON, possibly for Quimonios, the second is reconstructed as ...antaran, starting with either B, R or S.
According to Xavier Delamarre and Ranko Matasović, the meaning of Samonios is best explained as 'assembly', perhaps 'assembly of the living and the dead'.
Giamonios refers to winter. These two months divide the calendar into summer and winter seasons of six months, each season led off by a festival of several days marked with IVOS. This indicates an early version of the same traditional seasons as seen in later Celtic contexts: "For two divisions were formerly on the year, viz., summer from Beltaine, and winter from Samuin to Beltaine".
Allowing for variations between lunar and solar years and aligning the month names to the solar year's seasons, Samonios may have begun on the first quarter moon around May–June; if aligned to the modern Gaelic festivals Beltane, Lughnasadh, Samhain and Imbolc, Samonios might have begun around on the first quarter moon around April—May.

The lunar month

The Coligny calendar as reconstructed consisted of 16 columns and 4 rows, with two intercalary months given half a column each, resulting in a table of the 62 months of the 5-year cycle. Whether the 5 years of the calendar plaque is part of a Metonic cycle of 19 year or 30-year cycle, the full length of the calendar is still debated.
Each lunar year has 12 lunar months, six 30 day months, five 29 days months and a 29/30 day variable month. As synodic months are 29.53 days long, the calendar may overcome this by removing a day from a 30 day Equos month. The length of Equos may have been decided by the sighting of the first quarter moon, which start months in the calendar.
The first intercalary month is in year 1 at the start of the year before Samonios, the second appears between Cutios and Giamonios in year 3 in the middle of the year. The second has 30 days, the first is contested on whether it has 29 or 30 days. Intercalary months have set copying patterns from days across the months throughout the 5-year cycle to form their day notations.
McKay proposes the first intercalary month had 29 days, as the "30th" day of a 29 day month Cantlos, in year 1 would copy DIVERTOMV, a non-existant day. Olmsted notes it may be 30 days stating it is marked as a MATV month, and the remaining portion of the broken-off second digit of the Roman numeral for the last day potentially has a slant for XV instead of XIIII.

The start of the lunar month

The calendar month is broken into two halves with the term ATENOVX between them. The first half-month has 15 days. The second half-month has either 15 days, or 14 days with the term DIVERTOMV placed over the space for the 15th day. The notation patterns act as though this 'virtual' 15th day is present.
Pliny reported that the Celtic month began on the '6th day of the new moon'.
Classical writers counted from the day of the first visible moon, so the 6th day would be the first quarter moon, Day 1, the start of the calendar's month. The quarter moon with its D-shape is the only moment in the lunar phase that is easily identifiable by eye. The internal notations of the calendar confirm Pliny's statement, with a focus on the middle triplet of days in each half-month, days 7-8-9 and days 7a-8a-9a.

Full reconstruction

A full reconstruction of the calendar by McKay includes the latest information about the intercalary notations and the triple marks. Olmsted offers a previous reconstruction, which usefully aligns the notations with photographic images. RIG III presented an earlier in-depth description of terms with a reconstruction.

As a cycle of 19 years

If based on a Metonic cycle, this can be created with four 5-year cycles with the first year dropped and 30-day Equos months on Cycle years 1 and 5. All days and notations are lunisolar, moving within a 36 day range of a solar date.
The Metonic cycle, being 6940 whole days long, overruns the sun by 0.398396 days and the moon by 0.311620 days. As dates track phases of the moon, this would require a 30 day Equos month to be reduced to 29 days around every 61 years. As the moon would finish 0.0868 days ahead of the sun, the calendar after 219 years becomes a day ahead, requiring a 30-day month skipped after 6,569 years, or a 29-day month skipped after 6,350 years.

As a cycle of 30 years

The calendar can perform as a 30-year cycle, using six 5-year cycles with a 30-day intercalary month dropped once every 30 years. If part of a 30-year calendar, it overruns the lunar phase by 0.1515 days, requiring a day to be removed from a 30-day Equos roughly once every 198 years.
However, the internal months show a larger variation in accuracy for the lunar phase of nearly 48 hours, making the ability to track the lunar phase of 30-years notably less accurate. The lunar/solar difference is larger at 1.4172 days, requiring a 30-day month to be skipped every 198 years.
This relatively fast slippage against the solar year would also add to the already large lunisolar swing, for a total of 75 days before a possible adjustment, further aggravating the solar discrepancy, and displacing seasonal festivals by up to two and a half months.

Sample month

The month of SAMONIOS in year 2 is the only month without any missing fragments, thus preserving all of its notations. Most patterns of notations are known and can be reasonably reconstructed, though their purpose or significance is not fully understood.
The title starts with M declaring it is a month, followed by its name and type, thus M SAMON MAT reads as "M Samon Lucky/Good". The days are sorted in rows, with ATENOVX "Renewal" dividing the month in two parts after the 15th day. Each day has four columns for the peg-hole and the day's numeral, the triple-mark, the day's type and for any additional notations.
The count for the days are in Roman numerals with additive notation, after ATENOVX, the count is reset. The triple marks have either no value, ƚıı, ıƚı or ııƚ; some have M after the triple mark or in its place, which is part of the following day's type. Day types are vertically aligned with D "day" or N "night". Day notations that provide further information on whether days were swapped, additional notations for day type or festivals. The PRIN LOVDIN notation spans across type and notation.

Calendar notations

Several different notations, each with their own pattern, are placed sequentially on the 12 lunar months of the calendar, interacting according to certain rules with the notations before them, often replacing them. After the basic notations are set, many days' notations are then moved to other days, creating visual chaos. Finally, the days of the intercalary months are filled with notations copied from certain days in the 12 yearly months.
The notations, their patterns and interactions have gradually over the last century been identified by several key researchers, and what follows is a general, but not comprehensive, overview of each notation.

Numbering the days

Each month has two halves. The first half has days numbered from I to XV. The second half has either I–XV, or I–XIIII with the 15th day marked with DIVERTOMU. The term ATENOVX is placed between the two half-months. The patterns of the notations act as though the 30th day is always present. This means that in practice some months only have 29 days, but conceptually, all months have 30 days.

MAT and ANM months and their days

Six months are marked in their header as MAT "good, auspicious", and six as ANM "not good", based on comparisons with Middle Welsh mad and anfad and Old Irish mad and ni-mad..
The summer season has 4 MAT and 2 ANMAT months, the winter season has 2 and 4 respectively. MAT months have 30 days and ANMAT months have 29 days with the exception of Equos that can have 30 days in years 1 and 5.
Type------
Type123456
MATSAMRIVOGRCVTSIMAED
ANMGIAEQVELECANDVMANA

The order of the MAT and ANMAT months is determined by the seasons; MAT months start in Summer on Samonios and ANMAT months start in Winter on Giamonios. This order is used for determining the triple mark and PRINI LOVD/LAG notations across the days of the month.
MAT month days are initially assigned M D "good/auspicious day", and ANMAT month days are initially assigned D "neutral day". The terms M D and D refer to daylight hours in apposition to N "night". Any notation with N overwrites the full daytime notation, including triple marks, M D, D and D AMB.