Complex sentence: Cimiez Cathedral (also "Cathédrale Notre-Dame du Château"), was the former Roman Catholic cathedral of Nice in the south of France, sited on the hill of the castle overlooking the city (the "château de Nice").
Split into simpler sentences: Cimiez Cathedral (also "Cathédrale Notre-Dame du Château"), was a Roman Catholic cathedral in the southern town of Nice, France. It sat on the hill of the castle overlooking the city (the "château de Nice").