Complex sentence: Square Norman keeps built in stone became popular following the first such construction in Langeais in 994, the first such in Normandy; several were built in England and Wales after the conquest, by 1216 there were around 100 in the country.
Split into simpler sentences: Square Norman keeps built in stone became popular following the first such construction in Langeais in 994, the first such in Normandy. Several were built in England and Wales after the conquest; by 1216 there were around 100 in the country.