The Celtic population, while adopting many aspects of Roman material culture, maintained also many of its Celtic attributes. We have already seen that Jerome testifies to the continued use of the Celtic language among Treveri in the fourth century. Celtic religion too continued to flourish, alongside such imports as the imperial cult and the eastern cults, including Christianity, that soldiers and others introduced. Naturally the forms of the religion changed. Druids disappeared, but how important they had been, except in in aristocratic circles, is in any event disputed. Certainly their power and prestige did not long survive the end of Celtic independence, and Claudius actually proscribed them, Augustus having already forbidden Roman citizens to participate. Human sacrifice and head-hunting, which had been features of Celtic society in pre-Roman times, clearly did not survive the conquest either. But the popular religious beliefs and practices that can be shown still to flourish after the conquest, often in a strongly syncretistic form, must have had very deep roots. Celtic religion attached great importance to natural features considered to be sacred, such as mountains, springs and rivers, and there are many references to sacred groves.
Wells, Colin (1996 ). « Celts and Germans in the Rhineland », dans Miranda J. Green (dir.), The Celtic World, ch. 31, Routledge, Londres et New York, p. 612.