Complex sentence: It appears however that this community was the one previously established as St. Olav's Abbey, Stavanger, one of the earliest Augustinian monasteries in Norway if not the very earliest: the exact date of its foundation is unknown, but it was well established by 1160.
Split into simpler sentences: It appears however that this community was the one previously established as St. Olav's Abbey, Stavanger, one of the earliest Augustinian monasteries in Norway if not the very earliest. The exact date of its foundation is unknown, but it was well established by 1160.