Simplify the following text for a Grade 9 native English-speaking person.
Original: The abbey was extended in the 1190s by Abbot John de Cella ( also known as John of Wallingford ) ( 1195 â `` 1214 ) ; as the number of monks grew from fifty to over a hundred , the abbey was extended westwards with three bays added to the nave .
Simplified: The abbey was extended in the 1190s by Abbot John de Cella ( also known as John of Wallingford ) ( 1195 â `` 1214 ) .