Complex sentence: The Priory was a twelfth-century Augustinian foundation, dedicated to St Oswald supported initially by Robert de Lacy of Pontefract, and Thurstan of York.
Split into simpler sentences: The Priory was a twelfth-century Augustinian foundation, dedicated to St Oswald. It was supported initially by Robert de Lacy of Pontefract, and Thurstan of York.