Celtic polytheism, sometimes known as Celtic paganism, refers to the religious beliefs and practices of the ancient Celtic peoples of Western Europe prior to Christianization.
Celtic polytheism was animistic, believing in spirits existing in natural objects such as trees and rocks. Religious beliefs and practices of the Celts varied throughout the different Celtic lands, which included Ireland, Britain, Celtiberia, Gaul, areas along the Danube river, and Galatia; however there were commonalities shared by all.
Celtic mythology is the mythology of Celtic polytheism, apparently the religion of the Iron Age Celts. Like other Iron Age Europeans, the early Celts maintained a polytheistic mythology and religious structure.
Among Celts in close contact with Ancient Rome, such as the Gauls and Celtiberians, their mythology did not survive the Roman empire, their subsequent conversion to Christianity, and the loss of their Celtic languages.
[Music: 'Celtic Requiem Chant' by Elliot Simons; different than the 'Celtic Requiem']