The Tower of London: a Byte of History
"Raven in Front of Tower"

This, the main section of the Tower of London was built by William the Conqueror in 1066. A later English King declared that a dozen hungry ravens be kept on the grounds of the Tower, ostensibly to protect it, but also, as good luck charms. That decree was made in the 13th Century; it has been honored without interruption ever since. The original purpose of the ravens was to help eat and dispose of the dead. Of course, they no longer do that.