Ogham and the Tree Alphabet

Key takeaways: ogham (pronounced OH-am) is the earliest written Irish, a fourth-to-seventh-century monumental alphabet of strokes and notches; the inscriptions record names, not secrets; only five of the twenty letter names are securely trees; the medieval Bríatharogam kennings are the genuine poetic tradition; and the popular Celtic tree calendar is a 1948 invention by Robert Graves.

What is ogham and when was it used?

Ogham is among the most distinctive writing systems to emerge from the early Irish world: a script devised for the sounds of Primitive Irish, using groups of strokes and notches cut relative to a stem line (the natural angle or edge of a stone pillar, or a scored vertical line in manuscripts). Orthodox inscriptions on stone date from approximately the fourth to seventh centuries AD. Of roughly 400 known inscriptions confirmed by Ogham in 3D and Maynooth University, some 60 per cent are concentrated in Munster (Cork and Kerry especially), with further examples in Waterford, Kilkenny, Wales, Devon, Scotland, and the Isle of Man. All inscriptions follow a single epigraphic convention: the name of an individual in the genitive case, sometimes followed by a patronymic (maqi, “son of”), ancestor name, or kin-group identifier. Ogham stones are, in substance, the earliest durable written records of Irish personal names and the Irish language.

How does the ogham alphabet work?

The original alphabet comprises twenty feda (letters; the word fid means “wood/tree,” a terminological fact that encouraged later arboreal interpretation) arranged in four aicmí: Aicme Beithe (B-group: Beithe, Luis, Fern, Sail, Nin), Aicme hÚatha (H-group: hÚath, Dair, Tinne, Coll, Cert), Aicme Muine (M-group: Muin, Gort, nGétal, Straif, Ruis), and Aicme Ailme (A-group, the vowels: Ailm, Onn, Úr, Edad, Idad). Each letter is a group of one to five strokes or notches distinguished by its position relative to the stem line, and on stone the text is read upward along the pillar’s edge. Five forfeda (“extra letters”: Éabhadh, Óir, Uillenn, Iphín, Emancholl) were added in the manuscript period; only Éabhadh appears with any frequency on stone.

Are the ogham letters really named after trees?

The definitive scholarly analysis is Damian McManus’s A Guide to Ogam (1991) and his Ériu article (1988). The findings are clear and should anchor any interpretation.

Secure tree names (five): Beithe (birch), Fern (alder), Sail (willow), Dair (oak), Coll (hazel). These five have unambiguous arboreal primary meanings confirmed by etymology and medieval glosses.

Probable or possible (three more, per McManus): Onn (ash-tree, though the Auraicept misidentifies it as furze), Ailm (possibly pine, used in that sense in an eighth-century poem; etymology uncertain), Idad (probably a secondary form of iubhar, yew, supported by kennings).

Not trees at all: Luis, “blaze” or “herb” (later medieval tradition assigns rowan); Nin, “branch-fork”; hÚath, “fear, horror” (the hawthorn gloss is secondary folk-etymology); Tinne, “bar of metal, ingot” (holly is a medieval gloss, contradicted by the kennings themselves); Muin, “neck,” “ruse,” or “love” (vine is a later gloss); Gort, “field” (ivy is a later gloss); nGétal, “slaying”; Straif, “sulphur”; Ruis, “redness”; Úr, “earth, clay.”

Medieval scholars in the Auraicept were themselves aware of the problem: “Others say that it is not from men at all that the Ogham vowels are named but from trees, though some of these trees are not known to-day.” The arboreal interpretation was one competing theory among several, not an established ancient fact.

What are the Bríatharogam kennings?

The three Bríatharogam series (Old Irish two-word kennings glossing each letter’s name, edited in normalised Old Irish and translated by McManus 1988) are the richest authentic interpretive resource the tradition offers. They are attributed to legendary figures, Morann mac Moín (judge), Mac ind Óc (Óengus of the Tuatha Dé Danann), and Cú Chulainn, and survive in the three Ogam Tract versions, though the Cú Chulainn series is absent from the Book of Ballymote. A few examples illustrate their poetic character:

Dair (oak) / Morann: ardam dosae, “highest tree.” Straightforward. Fern (alder) / Morann: airenach fían, “vanguard of warriors” (alder was used for shields). Tinne (“metal bar”) / Morann: trian roith, “one third of a wheel.” No tree here: this is metallurgy. Gort (“field”) / Morann: milsiu féraib, “sweeter than grasses.” Pasture, not ivy. Beithe (birch) / Cú Chulainn: maise malach, “beauty of the eyebrow.” An oblique, bodily image.

These kennings give the letters genuine poetic life, but not the life of a tree zodiac.

What do the medieval manuscripts say?

The two main medieval sources are: Auraicept na n-Éces (“The Scholars’ Primer”), a grammatical tract surviving in the Book of Ballymote (c. 1391) and Yellow Book of Lecan, edited by Calder (Edinburgh, 1917); and In Lebor Ogaim (“The Book of Ogam”), the comprehensive ogham tract that immediately precedes the Auraicept in the Book of Ballymote, describing the basic alphabet, variant systems, and the Bríatharogam. The Auraicept attributes invention of the alphabet to Ogma, champion and poet of the Tuatha Dé Danann: “the father of Ogham is Ogma, the mother of Ogham is the hand or knife of Ogma.” The first text ever written in ogham, according to this tradition, was seven beithe strokes on a birch rod, a warning sent to Lug son of Ethliu about his wife’s abduction to the Otherworld.

Where can you see ogham stones in Mayo and Connacht?

County Mayo has at least ten recorded ogham stones, most 3D-scanned in 2022 through a Heritage Council/Mayo County Council project. Three are especially notable.

Breastagh (CIIC 10), barony of Tirawley near Killala, is the most accessible Mayo stone and a National Monument: a probable prehistoric standing stone re-used for an ogham inscription (3.66 x 0.76 x 0.60 m), discovered lying in a field in 1874 and re-erected by Sir Samuel Ferguson. The partially damaged inscription has been read by Macalister (CIIC I, 13-15) and McManus (1991, 53, 96-97) as recording a genealogical sequence with a syncopated form CORRB*RI pointing to a late sixth or early seventh century date; some scholars have connected the ancestor name with Amalgaid/Amlongad, king of Connacht (died c. 440-450 AD), though McManus urges caution given the stone’s condition.

Island (CIIC 1 / I-MAY-001), near Knock, is a sandstone pillar (1.80 m high) embedded in a barrow top, now nearly horizontal after a century of tilting. Inscription: CUNALEGI AVI CUNACANOS, “of Conlang, grandson of Conchaín,” linguistically dated to the fifth century AD; first published by John Rhys in 1898.

Rusheens West (CIIC 5), near Kilmovee, reads ALATTOS MAQI BR[---], “of Allatus son of Br…,” and stands beside a holy well dedicated to St Mobhí; it is among the linguistically earliest in Mayo, probably pre-sixth century. Not one of these stones encodes a calendar, a birth-sign, or a tree zodiac.

Where did the Celtic tree calendar come from?

The widespread “Celtic tree calendar” or “ogham birth-tree” system has no ancient authority. It was invented by Robert Graves in The White Goddess (Faber & Faber, 1948), where he identified thirteen consonants in a non-standard ogham ordering drawn from the seventeenth-century compilation Ogygia by Roderick O’Flaherty and assigned each to a month of a thirteen-month lunar year beginning on 23 December (a date that has no significance in any attested Irish traditional calendar, which begins at Samhain). He then equated those months with tree names and claimed the system was the basis of an ancient Druidic sacrificial calendar.

Peter Berresford Ellis’s “The Fabrication of ‘Celtic’ Astrology” (The Astrological Journal 39, no. 4, 1997) is the detailed published refutation. Ellis demonstrates: Graves had no knowledge of the Celtic languages; he dismissed expert advice from Macalister, the leading ogham scholar of the day; he relied on the distorted letter-ordering in O’Flaherty’s Ogygia rather than on the actual manuscript tradition; and the system is “a complete fabrication.” McManus’s 1988 Ériu analysis further establishes that the majority of letter names Graves treated as tree-names are not in fact arboreal in their primary meaning. None of the several hundred surviving ogham inscriptions mentions a calendar; none of the medieval ogham tracts assigns the letters to months. The “Celtic tree zodiac” circulating today on social media, in jewellery catalogues, and in neo-Druidic guides is a modern literary construct: an influential twentieth-century creative synthesis by an English poet. It can be acknowledged as exactly that, but it must not be presented as authentic ancient Irish tradition. The real ogham tradition, the stones, the kennings, the Ogma legend, is rich enough without supplementation.