There are nine castles in Greater Manchester, a metropolitan county in North West England. They consist of four motte-and-bailey castles, three fortified manor houses, an enclosure castle, and a possible shell keep. A motte-and-bailey castle is characterised by two elements: the motte is an artificial mound with a wooden stockade and stronghold on top, usually a stone keep or tower, while the bailey is a defended enclosure adjacent to the motte, typically enclosed by a ditch and a bank topped by a timber palisade or stone wall. Motte-and-bailey castles were the most common type of castle in England following the Norman Conquest. A shell keep was a motte with a stone wall rather than a wooden stockade on top; there would have been no tower within the walls. Four of Greater Manchester's castles are scheduled monuments: Buckton, Bury, Radcliffe Tower, and Watch Hill. A scheduled monument is a "nationally important" archaeological site or historic building, given protection against unauthorised change.
According to this paragraph, what was the most common type of castle in England following the Norman Conquest?
According to this text, the Motte-and-bailey castles were the most common following the Norman Conquest.