Complex sentence: The Lindisfarne Gospels are believed to the be the work of Eadfrith of Lindisfarne, bishop of Lindisfarne from 698, but these are not the only surviving Northumbrian illuminated manuscripts from Aldfrith's time.
Split into simpler sentences: The Lindisfarne Gospels are believed to the be the work of Eadfrith of Lindisfarne, bishop of Lindisfarne from 698. They are not the only surviving Northumbrian illuminated manuscripts from Aldfrith's time.