Tradition states that if the Ravens ever leave the Tower of London the kingdom and the tower will fall.
The tradition was born from a tale in the mythical Celtic Mabinogion texts of a Welsh giant Bran the Blessed. Bran went to battle against the Irish king who his sister Branwen had married and was being abused by. The battle was won, however Bran lost his life in the fight, on his command his men cut off his head which they carried around with them.
The head talked to them constantly giving them wise counsel, after a numbers of years they decided to bury the head under the Tower of London. It faced the shoreline so it could warn them against invaders coming up the channel. On hearing the tale the new King Arthur dug up Bran’s head and destroyed it citing he was the only protector required. However things didn’t go so well for Arthur after that with much of his country being overrun by the Saxons.
Bran is Welsh for Raven.
The tradition survives today with six (plus one spare) Ravens being kept at the Tower looked after the Raven Master their wings clipped to make sure they don’t go too far. A Yeoman ‘Raven Master’ cares for the Ravens feeding them daily raw meat along with bird biscuits dipped in blood.
Despite this pampered lifestyle some Ravens have gone absent without leave, one particular escapee was last seen outside a pub in the East End of London.