What was one of William the Conqueror major accomplishment as the King of England? William initiated many major changes. In 1085, in order to ascertain the extent of his new dominions and maximize taxation, William commissioned the compilation of the Domesday Book, a survey of England's productive capacity similar to a modern census. He also ordered many castles, keeps, and mots, among them the Tower of London, to be built across England to ensure that the rebellions by the English people or his own followers would not succeed. His conquest also led to Norman replacing English as the language of the ruling classes, for nearly 300 years. William is said to have deported some of the Anglo-Saxon land owning classes into slavery through Bristol. Many of the latter ended up in Umayyad Spain and Moorish lands. Ownership of nearly all land in England and titles to religious and public offices were given to Normans. Many surviving Anglo-Saxon nobles emigrated to other European kingdoms.