Ogham is a Celtic alphabet dating back to the fourth century. It is supposed to have originated among the Celtic tribes that migrated from the continent to Britain. The Celtic oracular alphabet is believed to be named for the Celtic God of communication and knowledge, Ogmos who was associated with the Greek Hermes and the Gaulish Ogmios.
The Ogham alphabet consists of twenty characters and each one is assigned a tree that was held scared by the Druids. Thus, each Ogham letter represents a particular tree and the attribute, feeling or essence that tree symbolizes. All of these simple characters are drawn using one to five angled or straight lines that are incised on a straight (vertical or horizontal) base line.
The use of the Ogham alphabet has never been very clear. Though there is no actual documentation to prove the symbols' original use, the Druids, NeoPagans and Wiccans use them as divination tools. The ancient Celts were spiritually progressive people who connected intensely with nature. Through the Ogham alphabet, they intertwined their writing system into communion with nature and used it for soulful reflection on the cosmic expressions manifest in the sacred trees.
Knowledge of Ogham is thought to have passed down the generations orally until the medieval times. The Book of Lecan (1416), Book of Ballymote (1391) and Book of Leinster (12th century) are some medieval manuscripts that record the use of Ogham as an alphabet system. The Ogham letters were usually inscribed on trees, sticks and stakes. However, the writing's surviving traces are in the form of stone inscriptions, generally on road markers and tombstones. Most of these have been found in the British Isles, in Wales and Southern Ireland. Some have also been discovered in places as far as Portugal and Spain.