By 950 , they were building stone keeps .
Norman barons built timber castles on earthen mounds , beginning the development of motte - and - bailey castles , and great stone churches in the Romanesque style of the Franks .
By 950 , barons were building stone keeps .
Norman barons built timber castles on earthen mounds , beginning the development of motte - and - bailey castles , and great stone churches in the Romanesque style of the Franks .