Complex sentence: About 836, Abbot Marquard founded a new monastery, Münstereifel; in 1017, Abbot Urald founded at Prüm a collegiate foundation for twelve priests.
Split into simpler sentences: About 836, Abbot Marquard founded a new monastery at Münstereifel. In 1017, Abbot Urald founded at Prüm a collegiate foundation for twelve priests.