William's final years were marked by difficulties in his continental domains, troubles with his son, Robert, and threatened invasions of England by the Danes. In 1086, he ordered the compilation of the "Domesday Book", a survey listing all the land-holdings in England along with their pre-Conquest and current holders. He died in September 1087 while leading a campaign in northern France, and was buried in Caen. His reign in England was marked by the construction of castles, settling a new Norman nobility on the land, and change in the composition of the English clergy. He did not try to integrate his various domains into one empire but continued to administer each part separately. His lands were divided after his death: Normandy went to Robert, and England went to his second surviving son, William Rufus.