All the Britons dye their bodies with woad, which produces a blue colour, and this give them a more terrifying appearance in battle. They wear their hair long, and shave the whole of their bodies except the head and the upper lip. Wives are shared between groups of ten or twelve men, especially between brothers and between fathers and sons; but the offspring of these unions are counted as the children of the man with whom a particular woman cohabitated first.
About 140 B.C.
As told by Winston Churchill in A History of the English-Speaking Peoples: The Birth of Britain
[I’m not certain I believe this. I mean, why would all the people shave their entire bodies except the head and upper lip? That’s a lot of shaving.
Interesting about the group marriage thing though.