What religion were the Celts?

Wikipedia: "The Celts had an indigenous polytheisticreligion and culture." "Polytheism is the belief in or worship of multiple deities, such as gods and goddesses." "While the regions under Roman rule adopted Christianity along with the rest of the Roman Empire, unconquered areas of Ireland and Scotland moved from Celtic polytheism to Celtic Christianity in the fifth century AD." "Celtic Christianity, or Insular Christianity (sometimes called the Celtic Church or the British Church or Irish Church) broadly refers to the Early Medieval Christian practice that developed in Britain and Ireland before and during the post-Roman period, when Germanic invasions sharply reduced contact between the broadly Celtic populations of Britons and Irish with Christians on the Continent until their subsequent conversion in the 5th and 6th centuries."