Celtic Polytheism

Celtic polytheism, commonly known as Celtic paganism, comprises the religious beliefs and practices adhered to by the Iron Age peoples of Western Europe now known as the Celts, roughly between 500 BCE and 500 CE, spanning the La Tène period and the Roman era, and in the case of the Insular Celts the British and Irish Iron Age.

Celtic polytheism was one of a larger group of Iron Age polytheistic religions of the Indo-European family. It comprised a large degree of variation both geographically and chronologically, although "behind this variety, broad structural similarities can be detected" allowing there to be "a basic religious homogeneity" amongst the Celtic peoples.

The Celtic pantheon consists of numerous recorded theonyms, both from Greco-Roman ethnography and from epigraphy. Among the most prominent ones are Teutatis, Taranis and Lugus. Figures from medieval Irish mythology have also been adduced by comparative mythology, interpreted as euhemerized versions of pre-Christian Insular deities. The most salient feature of Celtic religion as reflected in Roman historiography is their extensive practice of human sacrifice. According to Greek and Roman accounts, in Gaul, Britain and Ireland, there was a priestly caste of "magico-religious specialists" known as the druids, although very little is definitely known about them.

Following the Roman Empire's conquest of Gaul (58–51 BCE) and southern Britannia (43 CE), Celtic religious practices began to display elements of Romanisation, resulting in a syncretic Gallo-Roman culture with its own religious traditions with its own large set of deities, such as Cernunnos, Artio, Telesphorus, etc.

In the later 5th and the 6th centuries, Christianity became the dominant faith in the Celtic area, supplanting earlier religious traditions. However, it left a legacy in many of the Celtic nations, influencing later mythology, and served as the basis for a new religious movement, Celtic Neopaganism, in the 20th century.