Complex sentence: The cathedral of Troyes is a fine Gothic structure begun in the 12th, and completed in the 15th, century; the ancient collegiate Church of St. Urban is a Gothic building whose lightness of treatment reminds one of La Sainte-Chapelle at Paris.
Split into simpler sentences: The cathedral of Troyes is a fine Gothic structure begun in the 12th century, and completed in the 15th. The ancient collegiate Church of St. Urban is a Gothic building whose lightness of treatment reminds one of La Sainte-Chapelle at Paris.