Complex sentence: The monastery developed as the centre of a "large estate, a manor and a parish", and, by the early 9th century, it had become "extremely wealthy", but it then fell under the control of the archbishops of Canterbury.
Split into simpler sentences: The monastery developed as the centre of a large estate, a manor and a parish ", and, by the early 9th century, it had become" extremely wealthy. It then fell under the control of the archbishops of Canterbury.