Druids.
Their priests were called Druids: These lived in hollow trees, and committed not their mysteries to writing, but delivered them down by tradition, whereby they were in time wholly lost.
The Britons had wives in common, so many to a particular tribe or society, and the children were in common to that society.
About fifty years before Christ, Julius Caesar, the first Roman Emperor, having conquered Gaul or France, invaded Britain rather to increase his glory than conquests; for having overcome the natives in one or two battles, he returned.