The Tower of London doesn’t belong to the City, though it stood there for almost 900 years. It is more connected with the royal dynasties than with the world of business. It was originally built as a fortress to guard the river approaches to London. The Tower of London was begun by William the Conqueror in 1078 as a castle and palace. Since then it has been expanded, and used as an armoury, a zoo, a royal mint and a prison, a treasury and an observatory. A group of ravens live at the Tower. The tradition goes that if they disappear the building will collapse. For centuries a royal zoo was kept in the grounds. It once included a polar bear, which fished and swam in the moat. Now it is a museum and the Beefeaters (Yeoman Warders) guard the Tower. They used to be the monarch’s private bodyguard. Beefeater was a medieval nickname for well-fed servants. They wear a Tudor-style uniform of blue or red. They willingly show visitors the main places of interest. In some Tower rooms there are inscriptions carved on the walls by former prisoners. In Salt Tower you can see a complicated astronomical clock carved by a sixteenth century prisoner accused of black magic.