The early Celts lived in an enormous region, stretching from modern day Turkey through eastern and central Europe and westward and northward into much of Spain, Portugal, France, Belgium, Britain and Ireland. This wide spread made a difference in the religion of the Celts in various regions. The Celts worshiped a variety of deities, male and female. Some of these deities were associated with cosmos (sun, moon, stars), some with the local manifestations of the natural world (hills, rivers, wells, lakes, trees and mountains), others with cultural aspects such as wisdom and skill, healing and protection, magic, poetry, fertility and abundance.
The descriptions of the religions in Gaul are few. Three chapters of Caesar, a few lines from Diodorus, Mela, Strabo, Pliny and Lucian, and a statement from the Greek Timagenes, are reproduced in Ammianus Marcellinus. The preserved statues and inscriptions are also helpful. Caesar’s Commentarii de bello Gallico tells that the concepts of the Celts regarding the gods were much the same as others, meaning the Romans and Greeks. He tells that the most worshipped god was Mercury; however, the Gauls’ god was not named Mercury, but corresponded with the attributes of the Roman god. They regarded Mercury as the inventor of arts, presiding over trade and commerce, and the means of communication between people. After him, the Gauls honored Apollo, Mars, Jupiter, and Minerva. Of these gods, they held almost the same beliefs as the Romans did: Apollo drives away diseases, Minerva promotes handicrafts, Jupiter rules the heavens, and Mars controls war. Unfortunately, Caesar does not record the native names of the gods. In another article, Caesar records that the Gauls believe they are sprung from Pluto, the god of the lower world. This teaching comes from the Druids.
The Poet Lucian mentions three gods in the lines-
“Et quibus immites placatur sanguine diro
Teutates horrensque feris altaribus Esus
Et Taranis Scythicao non mitior Dianao”
We have here the grim Teutates, Esus with fearful sacrifice, and Taranis, whose altars were no less grisly than those of Scythian Diana. There are statues of Esus, but not much can be said about him. Teutates was probably a war god, defender of people. Taranis was the god corresponding with the Norse god Thor. Lucian mentions another god Ogmios, the god of letters and eloquence. Other names mentioned in writings and inscriptions are Bel/Belenus-god of the Druids, sun and health, and Belisama- goddess of art.
One notable feature of Celtic sculpture is the frequent conjunction of male deity and female consort, a protective god with a mother-goddess who ensures the fertility of the land. It is nearly impossible to distinguish clearly between the individual goddesses and these mother-goddesses, matres or matronae, who figure so frequently in Celtic iconography, most often in Irish tradition. These goddesses and mother-goddesses are identified with fertility and with the seasonal cycle of nature, and both drew much of their power from the old concept of a great goddess, mother of all the gods. Welsh and Irish traditions preserve many variations on a basic triadic relationship of divine mother, father, and son. The goddess appears, for example, in Welsh as Modron (from Matrona, “Divine Mother”) and Rhiannon (“Divine Queen”) and in Irish as Boann and Macha. Her partner is represented by the Gaulish father-figure Sucellos, his Irish counterpart Dagda, and the Welsh Teyrnon (“Divine Lord”), and her son by the Welsh Mabon (from Maponos, “Divine Son”) and Pryderi and the Irish Oenghus and Mac ind Óg, among others.
Druids were a type of priesthood in the Celtic religion. The name itself means “knowing the oak tree” and may derive from druidic ritual. Caesar tells that the druids avoided manual labor and paid no taxes. As already mentioned, human sacrifice was practiced, but was forbidden by Tiberius and Claudius.
Sources:
Sharon Paice MacLeod Celtic Myth and Religion: A study of traditional belief, with newly translated prayers, poems and songs (McFarland, 2011), 9
Alexander MacBain Celtic Mythology and religion (Cosimo Inc. 2005), 61
Proinsias Mac Cana, Myles Dillon Celtic Religion, Encyclopedia Britannica
Alexander MacBain Idem, 64,65