The Caractacus Stone, Winsford Hill, Exmoor.
Caractacus was a chieftain who led the resistance to Roman invasion of Britain in 43 AD. He was eventually captured and taken to Rome where the Emperor Claudius spared his life. This stone bears a Latin inscription datable to around 500 AD which is believed to refer to the family of Caractacus. Today the stone is protected by having a small shelter built over it.
See :
http://en.wikipedia.org/wiki/Caratacus