The ogham alphabet was a Celtic writing system used from the 4th to 6th centuries AD and may be as old as the 1st century AD. It was used to write Primitve and Old Irish, Pictish, Old Welsh, and Latin. It is found on rock monuments throughout the British Isles where the Celtic people resided, but was also used on wooden sticks, stakes, and even trees. Each letter is indicated by a series of strikes along a solid vertical line, usually indicated by the edge of the surface it was written on. Later on the alphabet was used on paper manuscripts, at which point a horizontal line was replaced with the vertical one.
The Book of Ballymote, which was written in the 14th century, was the first to assign each letter of the ogham alphabet to a different tree. There doesn’t seem to be much existence of this method dating any earlier than the publication of The Book of Ballymote and scholars seem to not put much stock in its accuracy. As you can see above, the letters were originally separated into four groups, or aicmi (the singular form of which is acime), and a fifth group was added later once the alphabet was beginning to be used in manuscripts. When written vertically, sentences are read bottom to top and left to right. Horizontally, it is read left right. So in the example to the right, it reads “bat wings and skeleton keys” from bottom to top and the example below reads “Rae Sengele” from left to right.
In the 20th century, Robert Graves, an English poet, made the argument that some of the ogham letters were assigned to the cycles of the moon, creating the Celtic Tree Calender. There is some controversy over this, but we’ll get into that next week.