Ogham was the ancient alphabet of the Celts. Ogham is thought to have been invented in southern Ireland, although examples have been found in many parts of the British Isles. Letters were composed of straight or slanting lines, incised onto the edges of wooden or stone blocks. Evidence suggests that it was in common use from c. AD 300 until the seventh century, although some authorities believe that it may have been used even earlier on perishable materials. The Irish sagas tell of great libraries of ogham texts, recorded on pieces of bark, but no traces of these have been found.
In the Táin, Cú Chulainn issued challenges to the Connacht men in ogham, carved on standing stones. The ogham was also believed to have magical properties, and druids used them in divination. The system was named after Ogma, the god of eloquence, prized by the Celts who rated word-power higher than physical prowess.
Imbolc was the second of the Celtic seasonal festivals, covering the months of February, March and April. The chief rituals were carried out on 1 February and had strong associations with fertility. In pastoral terms, they were linked with lambing and the lactation of ewes. The festival was also devoted to the powerful triple-goddess, Brigid. In her different aspects, she was influential in the fields of healing, poetry and smithcraft. Poets regarded her as the source of literary inspiration and her protection was frequently invoked by mothers in childbirth. In Ireland, she was much revered by the filidh (sages), who recognized her gift of prophecy.
The cult of Brigid was probably connected with the worship of Brigantia, a northern British deity, and also with the Irish saint of the same name. It can be no coincidence that the latter's feast day is celebrated on 1 February, the same day as Imbolc.