The word "Britain" is derived from "Pretani" meaning "painted", originally because most Britons had tattoos.
The first proven tattoos in history date back around 5,000 years to the marks on Otzi the Iceman, a mummy found in the Alps straddling Austria and Italy. But in Europe, it became the early Britons who made the art famous: when the Romans invaded in 55 BC, they found the natives to be resplendent in body art.
As Caesar wrote in his account of the Gallic Wars, "All the Britons dye themselves with woad, which produces a blue color, and makes their appearance in battle more terrible." Such was the effect of their appearance that they became known throughout Europe as the Pretani, a Celtic word meaning the 'painted' or the 'tattooed' ones. From that, the name Britain was eventually derived.