The Legend of Branwen
Matholwch, King of Ireland, wed Branwen, sister of King Bran. At first, all went well and a son was born to the couple but, in the second year, he began to mistreat her.
In secret, Branwen reared a starling and taught it to recognise her brother. She fastened a letter under its wing and sent it flying to the King. The angry King Bran gathered a large army and a fleet of ships and set off for Ireland. There followed a mighty battle, during which King Bran was mortally wounded. As he lay dying, he said "Cut off my head and bury it on the white mound of London, facing towards France. Whilst it remains, no harm shall come to the island of the mighty from across the sea".
That is why, even today, birds are kept at the Tower of London (Bran means crow in Welsh), in accordance with the prophecy of King Bran; for without them, the White Tower and the British monarchy will fall.
Only Branwen and seven men returned to Wales and, when she died, she was buried beneath a standing stone on Anglesey.