Ogham Alphabet

"In ancient times, the Druids carved messages into the sides of large rectangular stones using the alphabet created by a young Celtic man named Ogma. The Ogham alphabet comprises twenty characters and most are named after trees."

The base of each letter is a vertical line and characters are lines branching to the right and the left from it, like a tree. Because of this, letters were named after trees: Ailm is pine, Beith is birch, Coll is hazel, and so on. The whole alphabet is therefore considered a forest.

"Individual trees held high symbolic significance, so the forest alphabet was deemed a repository of wisdom. The word for 'knowledge' also means 'wood'."

Inscriptions are read from the bottom up, the way a tree grows.

Source: The Element Encyclopedia of the Celts, by Rodney Castleden