Although a small number of castles had been built in England during the 1050s, after the conquest the Normans began to build timber motte and bailey and ringwork castles in large numbers to control their newly occupied territories. During the 12th century the Normans began to build more castles in stone, with characteristic square keeps that supported both military and political functions. Royal castles were used to control key towns and forests, whilst baronial castles were used by the Norman lords to control their widespread estates; a feudal system called the castle-guard was sometimes used to provide garrisons. Castles and sieges continued to grow in military sophistication during the 12th century, and in the 13th century new defensive town walls were constructed across England.