Ancient Celtic religion
Greek and Roman records

Various Greek and Roman writers of the ancient world commented on the Celts and their beliefs. Barry Cunliffe stated that "the Greek and Roman texts provide a number of pertinent observations, but these are at best anecdotal, offered largely as a colourful background by writers whose prime intention was to communicate other messages." The Roman general Julius Caesar, when leading the conquering armies of the Roman Republic against Celtic Gaul, made various descriptions of the inhabitants, though some of his claims, such as that the Druids practised human sacrifice by burning people in wicker men, have come under scrutiny by modern scholars.

However, the key problem with the use of these sources is that they were often biased against the Celts, whom the classical peoples viewed as "barbarians". In the case of the Romans who conquered several Celtic realms, they would have likely been biased in favour of making the Celts look uncivilised, thereby giving the "civilised" Romans more reason to conquer them.
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