The Ogham script recorded the earliest Old Irish texts dating between the 3rd and the 6th century CE. Ogham inscriptions are found exclusively in Ireland, Scotland, and Wales. Mostly they are genealogical inscriptions in the form of "X son of Y" on corners of large stone slabs. After the 6th century CE, Old Irish was written with the Roman alphabet, and Ogham disappeared from general but the knowledge must have been preserved in some form because our knowledge of Ogham comes from the chapter Auraicept na n-Éces in the 15th-century work The Book of Ballymote (Leabhar Bhaile an Mhóta), which also contains geneologies, mythologies, and histories of Ireland.
Various opinions exist on the exact origin of ogham. Some claim that it stemmed from a cryptic way of writing runes, some say that it was inspired from the Roman alphabet, and yet others hold that it was independently invented.
The Ogham letters are divided into four groups, each containing five letters. This yields a total of 20 Ogham letters.
When inscribed on stones, Ogham is written vertically from bottom to top. The following chart lists all Ogham letters in their vertical forms, along with their Old Irish names and meanings.
Sometimes the vowels use dots rather than lines intersecting the vertical axis.
In some cases, mostly in manuscripts, Ogham is written horizontally from right to left.
The ordering of the letters is a mystery, as it does not correspond to neither Roman nor runic letter orders. It appears to have some phonetic basis. For instance, the fourth group contains all vowels, and the vowels are arranged according to their position in the mouth. The vowel /a/ is a central vowel, /o/ and /u/ are back vowels, and /e/ and /i/ are front vowels. Another possible phonetic layout is the second group, which contains all stop consonants except for the consonant /h/.
In Auraicept na n-Éces, a fifth group of letters called forfeda is also listed. These extra letters did not appear in stone inscriptions before the 6th century CE, and most likely were added to represent new sounds introduced by natural changes in the Irish language after the 6th century CE.
The following is an Ogham inscription from County Kerry, Ireland. It is fairly typical in that its text is genealogical information.
Many thanks to Prof Curtis Clark of Cal Poly Pomona for his Ogham font, which was used to create the images on this page.