The Celtic Tree Calendar

The raw material is real and the calendar is not. Medieval Irish grammatical and scholarly tracts record the letters of the ogham alphabet together with glosses, and among the several kinds of gloss are lists that attach a tree or a plant to each letter. Those lists are word lore: mnemonic kennings for the letters, of the same type as the lists that attach birds, colours, fortresses and occupations to them. They are not a division of time and no medieval text uses them as one.

Robert Graves took the tree glosses, selected thirteen of them, assigned each a lunar month and built a calendar. He was writing a book of poetic argument rather than of scholarship, said so, and reached his conclusions by association and intuition, which he defended as the proper method for the subject. The arithmetic does not survive contact with the alphabet either. Ogham has twenty letters in its basic form, arranged in four groups of five, with further characters added later, so producing thirteen months requires deciding which letters to use, which to leave out and in what order to run them. Every one of those decisions is Graves's, and none of them is reported from a source. The atlas records the medieval tree glosses as genuine material of a genuine tradition, and the calendar built from them as a twentieth century composition by a named author whose method is on the record.

Being modern has not made it marginal. The tree calendar was taken up by modern Druid orders, by Wiccan and broader pagan practice, and by a popular tree astrology in which a birth date yields a tree and a character reading, and it circulates in books, greeting cards, jewellery and websites with the word Celtic attached. Large numbers of people have encountered it, and a fair number keep it.

Historians of Druidry have documented the invention in detail, both the medieval sources and what Graves did with them, and the finding is not disputed among specialists. It sits alongside a good deal of other modern material presented as ancient Celtic religion, an area where the gap between what survives and what circulates is unusually wide. The atlas keeps the entry and states both facts together, because a scheme with a large modern following is a real object of study whatever its pedigree, and because quietly omitting it would leave a reader who meets it elsewhere, as most people will, with nothing to check it against. Recording an invention as an invention is more useful than pretending it is not there. What the calendar is not is evidence for how any ancient Celtic speaking people organised the year. That question is poorly documented, rests on a small number of difficult sources, and is entirely separate from this one.