sometimes there is a tympanum at the back of the head of the arch, which may feature sculpture representing a Biblical scene. Norman windows are mostly small and narrow, generally of a single round-headed light; but sometimes, especially in a bell tower, divided by a shaft into two lights. Normandy Viking invaders arrived at the mouth of the river Seine in 911, at a time when Franks were fighting on horseback and Frankish lords were building castles. Over the next century the population of the territory ceded to the Vikings now called Normans, adopted these customs as well as Christianity and the langue d'oïl. 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, they were building stone keeps. The Normans were among the most travelled peoples of Europe, exposing them to a wide variety of cultural influences which became incorporated in their art and architecture. They elaborated on the early Christian basilica plan. Originally longitudinal with side aisles and an apse they began to add in towers, as at the Church of Saint-Étienne at Caen, in 1067. This would eventually form a model for the larger English cathedrals some 20 years later. England In England, Norman nobles and bishops had influence before the Norman Conquest of 1066, and Norman influences affected late Anglo-Saxon architecture. Edward the Confessor was brought up in Normandy and in 1042 brought masons to work on the first Romanesque building in England, Westminster Abbey. In 1051 he brought in Norman knights who built "motte" castles as a defence against the Welsh. Following the invasion, Normans rapidly constructed motte-and-bailey castles along with churches, abbeys, and more elaborate fortifications such as Norman stone keeps. The buildings show massive proportions in simple geometries using small bands of sculpture. Paying attention to the concentrated spaces of capitals and round doorways as well as the tympanum under an arch. The "Norman arch" is the rounded, often with mouldings carved or incised onto it for decoration. chevron patterns, frequently termed "zig-zag mouldings", were a frequent signature of the Normans. The cruciform churches often had deep chancels and a square crossing tower which has remained a feature of English ecclesiastical architecture. Hundreds of parish churches were built and the great English cathedrals were founded from 1083. After a fire damaged Canterbury Cathedral in 1174 Norman