Complex sentence: The new town was founded at the foot of the mountain, by the shore, by Roger II of Sicily in 1131, and the cathedral was begun in the same year in a style of Norman architecture which would be more accurately called Sicilian Romanesque.
Split into simpler sentences: The new town was founded at the foot of the mountain, by the shore, by Roger II of Sicily in 1131, and the cathedral was begun in the same year. The Cathedral, begun in 1131, in a style of Norman architecture which would be more accurately called Sicilian Romanesque.