Named for Ogmos, the Celtic god of knowledge and communication, the Ogham [o-ehm] alphabet dates from the 4th century. Consisting of twenty letters, each named for a different tree believed sacred to the Druids, the proper name for the Ogham alphabet was Beithe Luis Fern, so named for the first three letters of the alphabet. Each letter is made up of one to five straight or angled lines incised on a straight base line. Written vertically on stone carvings and ruins and horizontally on parchment, Ogham is the first known written language of Ireland. Surviving examples of Ogham exist as stone carvings, usually on tombstones and road markers, and have been found all over the Celtic Isles and as far as Spain and Portugal. Ogham was carved and read from bottom to top and occasionally from right to left.