The Druids did not use writing ("by the hand of man") to record their stories and traditions. The Ogham tree letters, however, were used to record druidical works. Each Ogham letter was represented by a single leaf from the tree bearing its name. Sacred Druidic verse was represented this way because trees were considered "of the gods."
Traditions say the first use of Ogham was as a warning to Lugh, saying that his wife would be carried away into faeryland unless birch guard her.