Ancient Celts did not believe in a monotheistic god but in a pantheon of nature. Gods protected the clan and gave strength in war while Goddesses protected the home and brought fertility. Gods also controlled the natural elements and had to be propitiated through offerings and sacrifices. Human and animal sacrifice were offered although the former was rare and only in times of great need.
Strength, Power and Fertility represented a special trinity of the Gods for the Irish Celts. Druids designated special places of worship to Gods and Goddesses adjacent to water and groves of trees, usually oak.
Among the gods were:
Brigit – Goddess of learning and fertility and healing powers, later adopted by the Irish branch of Christianity under the same name.
Lugh mac Ethnenn – One of the principal Celtic gods of the Tuatha Dé Danann; He was the divine father of Sétanta. He is god of the harvest, a sun god. Lugnasa was the festival held in his honour, halfway between the summer solstice and autumn equinox. In the Táin, he casts a spell on Deichtine after she swallows the mayfly and goes to Brúgh na Bóinne for the winter solstice where Sétanta is conceived.
The Morrígna – were the triple goddesses associated with and personified by, the frenzied havoc of war. They fought on the side of the mythical Tuatha De Danann against both the Fir Bolg and the Formorions. Using their magic, the three sisters / daughters would incite fear and confusion among one side or the other, causing many to fall, in fear, on their own weapons.
Badb—meaning “crow“— (scaldy crow) was one of a trio of war goddesses making up the Mórrígna. One of the “Great Queens” or war goddess, Badb often assumed the form of a screaming crow, causing fear and confusion among warriors in order to move the tide of battle to her favoured side. Badb would also appear before a battle to foreshadow the extent of the carnage to come or to predict the death of certain warriors. Her wailing cries, similar to the cries of the later “bean-sídhe” (banshee) popular in Irish folklore was common among the dead on the battlefield.
Macha – Together with Badb and Nemain, she made up the trio of war/fertility goddesses, known as the Mórrígna in the Tuatha Dé Danann. In the Táin, she tries to seduce Sétanta but is rejected (it is not for a woman’s arse that I undertook this fight, he claimed) and she cursed him threefold; Sétanta wounded her threefold but she tricks him into curing her threefold. Daughter of Sainrith mac Imbaith, and consort to Crunniuc, son of Agnoman, she was the one to lay the original curse on the Ulaidh. Macha was often associated with horses – Sétanta was born at the same time as the colts, one of which was called the Grey of Macha or Liath Macha
Nemain – was the third war spirit of the trinity, and, in the Táin, attacks Medb’s army after they had already been harassed by Sétanta. She sometimes appears as a bean nighe, the weeping washer, by a river, washing the clothes or entrails of a doomed warrior.
Together with her sisters, they often appeared decorated with “mast” of acorn crops – a synonym for human heads harvested by the trio.
Red Branch Chronicles 