The period beginning in 1066 with Duke William of Normandy’s victory over the English at the Battle of Hastings. As William I (1066–87) he established a military superiority over the English, rebellions were crushed (1067–71), and about 5000 castles were constructed by the time of his death. England’s frontiers were protected, first by marcher lords and then through conquest. Ruthless attention to detail characterized the Norman approach to government. English institutions were either retained and developed (such as the treasury, the king’s council, the king’s peace, sheriffs, and the shire system) or replaced with Norman versions. Not all changes were popular with the English, who had already lost heavily in terms of status, land holdings, and public office. Taxation was heavier, forest laws were harsh and outside the common law. Norman efficiency produced the unique survey recorded in Domesday Book (1086), though it owed a great deal to existing English records. The language of government and of the court was Norman French. England prospered commercially: its towns grew, as did its population. Many of these developments would probably have arisen without Norman rule—as is also true of the reorganization of the English Church under Archbishop Lanfranc—but the rapid nature of these changes owed most to the Norman Conquest. In architecture the Norman style, characterized by rounded arches and heavy pillars was introduced after the Conquest.