TheCeltic calendar refers to thecalendar systems used by ancientCelts to define the beginning and length of the day, week, month, season, quarter-day, and festivals. TheColigny calendar, manufactured in 2nd century CERoman Gaul (modernFrance), is one of the most notable representations of a Celtic calendar.^[1]

TheColigny calendar is the oldest known Celticlunisolar ritual calendar. It was discovered inColigny, France, and is now on display in the Palais des ArtsGallo-Roman museum, Lyon. It dates to the end of the second century CE,^[2] when theRoman Empire imposed the use of theJulian Calendar inRoman Gaul. The calendar was originally a single huge plate, but it survives only in fragments.^[3] It is inscribed in theGaulish language using theLatin alphabet and usesRoman numerals.

The Coligny Calendar reconciles the cycles of the moon and sun. The Coligny calendar considers thephases of the moon to be important, and each month always begins with the same lunar phase. The calendar uses a mathematical arrangement to keep a normal 12-month calendar synchronized with the moon and which keeps the whole system synchronized by adding anintercalary month every 2.5 years. The Coligny calendar registers a 5-year cycle of 62 lunar months, divided into a "bright" and a "dark"fortnight (or half of a moon cycle) each. The internal notations show that the months began with the first quarter moon, and a 13th intercalary month was added every 2.5 years to align the lunations with the solar year.

The astronomical basis of the Coligny plaque's calendar year may be far older than the plaque itself, ascalendars are usually more conservative than rites andcults. The date of its inception is unknown, but correspondences ofInsular Celtic andContinental Celtic calendars suggest that some early form may date to the earlierIron Age. The Coligny calendar achieves a complex synchronisation of the solar and lunar months. Whether it does this for philosophical or practical reasons, it points to a considerable degree of sophistication.

Among theInsular Celts, the year was divided into a light half and a dark half. As the day was seen as beginning at sunset, so the year was seen as beginning with the arrival of the darkness, atCalan Gaeaf /Samhain (around 1 November in the modern calendar).^[4] The light half of the year started atCalan Haf/Bealtaine (around 1 May, modern calendar). This observance of festivals beginning the evening before the festival day is still seen in the celebrations and folkloric practices among theGaels, such as the traditions ofOíche Shamhna (Samhain Eve) among the Irish andOidhche Shamhna among theScots.^[5][6]

Julius Caesar said in hisGallic Wars: "[the Gaulish Celts] keep birthdays and the beginnings of months and years in such an order that the day follows the night." Longer periods were reckoned in nights, as in the surviving English term fortnight meaning two weeks, and the obsoletese'nnight meaning one week.

TheLaws of Hywel Dda (in editions surviving from the 12th and 13th centuries) make repeated references to periods ofnine days (nawfed dydd), rather than the "eight nights" that make up the current wordwythnos.^[7]

Many calendrical and time-keeping terms used in the medieval and modern Celtic languages were borrowed from Latin and reflect the influence of Roman culture andChristianity on the Insular Celts. The words borrowed include the month namesJanuarius (Old IrishEnáir, IrishEanáir, WelshIonawr),Februarius (Old IrishFebra, IrishFeabhra, WelshChwefror),Martius (Old IrishMart, WelshMawrth),Aprilius (Old IrishApréil, IrishAibreán, WelshEbrill),Maius (WelshMai),Augustus (Old IrishAuguist, WelshAwst); the names for the days of the week,Solis,Lunae,Martis,Mercurii,Jovis,Veneris,Saturni; the termsseptimana "week" (Old Irishsechtmain, Bretonsizun, Cornishseithun),kalendae "first day of the month" (Old Irishcallann, Welshcalan, Bretonkala),tempore "time" (Welshamser),matutina "morning" (Cornishmetin, Irishmaidin),vespera "evening",nona "noon" (Welshnawn, Irishnóin), andôra "hour" (Welshawr, Bretoneur, Irishuair).^[8][9]

A number of native Celtic terms survived the adoption of the Roman/Christian calendar, however:

In someNeopagan religions, a "Celtic calendar" loosely based on that ofMedieval Ireland is observed for purposes ofritual. Adherents ofReconstructionist traditions may celebrate the fourGaelic festivals ofSamhain,Imbolc,Beltane, andLughnasadh.^[12][13]

Some eclectic Neopagans, such asWiccans, combine the Gaelic fire festivals with solstices and equinox celebrations derived from non-Celtic cultures to produce the Wiccan modernWheel of the Year.^[14]: 337 Some eclectic Neopagans are also influenced byRobert Graves' "Celtic Tree Calendar", which has no foundation in historical calendars or actual ancientCeltic Astrology, instead being derived from Graves' extrapolation ofThe Song of Amergin.^[14]: 145

• Coligny calendar
• Irish calendar (Gaelic calendar)
• Welsh holidays

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• Brunaux, Jean-Louis (1986).Les Gaulois: Sanctuaires et Rites [The Gauls: Sanctuaries and ceremonies]. Paris: Editions Errance.
• Duval, Paul-Marie; Pinault, Georges (eds.). "The calendars of Coligny (73 fragments) and Villards d'Heria (8 fragments)".Recueil des Inscriptions Gauloises (R.I.G.). Vol. 3.
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• Jackson, Kenneth Hurlstone (1967).A Historical Phonology of Breton. Dublin: Dublin Institute for Advanced Studies.
• Jenner, Henry (1982).A Handbook of the Cornish Language. New York: AMS Press. pp. 203 ff.ISBN 0404175570. (reprint of 1904 ed.)
• Koch, John, ed. (2006). "Calendar, Celtic".Celtic Culture: a historical encyclopaedia. Santa Barbara: ABC-Clio. pp. 330–332.
• Lambert, Pierre-Yves (1995).La langue gauloise [The Gaulish Language]. Paris: Editions Errance. pp. 109–115.
• Loth, Joseph (1892).Les mots latins dans les langues brittoniques. Paris: E. Bouillon.
• Matasović, Ranko (2009).Etymological Dictionary of Proto-Celtic. Brill Academic Publishers.
• Nance, Robert Morton, ed. (1955).A Cornish-English Dictionary. Marazion: Worden, for the Federation of Old Cornwall Societies.
• Pokorny, Julius (1959–1969).Indogermanisches etymologisches Wörterbuch [[proto-]Indo-Germanic Etymological Dictionary]. Bern-München.{{cite book}}: CS1 maint: location missing publisher (link)
• Schrijver, Peter (1995).Studies in British Celtic Historical Phonology. Amsterdam: Rodopi.
• Vendryes, Joseph; Bachallery, Édouard; Lambert, Pierre-Yves (1959–1996).Lexique étymologique de l'irlandais ancien [Etymological Dictionary of the Ancient Language of Ireland]. Dublin: Dublin Institute for Advanced Studies.

• Celtic art
• Celtic mythology
• Culture of Ireland
• Specific calendars

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