The Library Kids : Celtic Writing System of Ogham

The twenty standard letters of the Ogham alphabet and the five forfeda. The box on the left shows the consonants, and the box on the right shows the vowels (both non-IPA). The letter labelled IA (Ifín) earlier had the value of p. An additional (secondary) letter p is shown as 26th character (peith). Note: This is the vertical writing of Ogham. In the horizontal form, the right side would face downward.

Ogham is an ancient Celtic method of writing that has various legends associated with it. Per Wikipedia:

According to the 11th-century Lebor Gabála Érenn, the 14th-century Auraicept na n-Éces, and other Medieval Irish folklore, ogham was first invented soon after the fall of the Tower of Babel, along with the Gaelic language, by the legendary Scythian king, Fenius Farsa. According to the Auraicept, Fenius journeyed from Scythia together with Goídel mac Ethéoir, Íar mac Nema and a retinue of 72 scholars. They came to the plain of Shinar to study the confused languages at Nimrod's tower (the Tower of Babel). Finding that they had already been dispersed, Fenius sent his scholars to study them, staying at the tower, co-ordinating the effort. After ten years, the investigations were complete, and Fenius created in Bérla tóbaide "the selected language", taking the best of each of the confused tongues, which he called Goídelc, Goidelic, after Goídel mac Ethéoir. He also created extensions of Goídelc, called Bérla Féne, after himself, Íarmberla, after Íar mac Nema, and others, and the Beithe-luis-nuin (the ogham) as a perfected writing system for his languages. The names he gave to the letters were those of his 25 best scholars.

Alternatively, the Ogam Tract credits Ogma mac Elathan (Ogmios) with the script's invention. Ogma was skilled in speech and poetry, and created the system for the learned, to the exclusion of rustics and fools. The first message written in Ogam were seven b's on a birch, sent as a warning to Lug mac Elathan, meaning: "your wife will be carried away seven times to the otherworld unless the birch protects her". For this reason, the letter b is said to be named after the birch, and In Lebor Ogaim goes on to tell the tradition that all letters were named after trees, a claim also referred to by the Auraicept as an alternative to the naming after Fenius' disciples.

Ogham is sometimes called the "Celtic Tree Alphabet", based on a high medieval Bríatharogam tradition ascribing names of trees to the individual letters. The etymology of the word ogam or ogham remains unclear. One possible origin is from the Irish og-úaim 'point-seam', referring to the seam made by the point of a sharp weapon.^[4]