On Christmas Day 1066 William Duke of Normandy was crowned King of England in Westminster Abbey, some two months after his victory over the Saxon King Harold at Hastings. At once William ordered the building of fortifications to help secure London, the chief city of his new kingdom. One of these earth-and-timber castles was erected in the south-east comer of the Roman city walls, to command the River Thames as well as the city. To close off the angle between the walls and complete the bailey, or yard, of the new castle, the Normans made a ditch and bank surmounted by a palisade. Ten years later, then in full control of England, William determined to transform this simple fort into a massive palace-fortress. A great stone tower was built and at once entitled the Tower of London. Later, as the castle was enlarged around it, that name was to be given to the entire fortress, and the great central tower became known as the White Tower.