Ever watch Inside the Tower of London? Fun series!

The Mabinogion tells us that the site of the White Tower is also the burial place of the head of Bran the Blessed, once King of the Island of the Mighty (Brtain), who was mortally wounded in battle with the Irish. He told his brother Manawydan to cut off his head and take it back to Britain with the six other survivors of the battle. The head continued to talk and sing, as well as magcally providing hospitality for its companions, first for seven years at Harlech, then for eighty years at Dyfed (durig which time none of them aged). But when one of the companions broke the geas the head fell silent. It was taken to a 'White Hill', supposedly where the Tower now stands, and buried facing France to guard against invasion.

Bran is Welsh for 'crow' or 'raven'.