Complex sentence: In the 13th century, Pierre de Wessencourt, the 25th abbot, built the "Sainte-Chapelle" at the chevet of the abbey church, which closely resembled the Sainte-Chapelle in Paris, built twelve years earlier.
Split into simpler sentences: In the 13th century, Pierre de Wessencourt, the 25th abbé, built the Sainte-Chapelle at the chevet of the abbey. This addition closely resembled the Sainte-Chapelle in Paris, built twelve years earlier.