hortly after becoming King of England in 1066 William the Conqueror constructed an earth and timber castle in the corner of the old Roman city walls of London. Around this was dug a ditch and a bank was formed with a wooden palisade on top. From this point William could command London and monitor all ship movements up and down the river Thames. About ten years after the Conquest William decided to strengthen the castle. Gundulf the Bishop of Rochester, whose building techniques were admired by William, was brought to London to design and build the new keep at the Tower of London. The foundations were laid in 1078 and the structure was completed in the reign of William Rufus in 1097. This is now known as the White Tower after Henry III whitewashed the exterior. The tower has walls fifteen feet thick at the base, a chapel dedicated to St John the Evangelist taking up two of the upper floors, a 40 foot deep well and more than one crypt.