Complex sentence: Ilbert founded inside his fortress a collegiate chapel, dedicated to St. Clement, and also built the foundation for the abbey of St. Oswald at Nostell, completed by his eldest son and heir, Robert De Lacy.
Split into simpler sentences: Ilbert founded inside his fortress a collegiate chapel, dedicated to St. Clement. He also built the foundation for the abbey of St. Oswald at Nostell, completed by his eldest son and heir, Robert De Lacy.