The tower was originally built to one storey above the origional roofline. Abbot William Marshall added the upper lantern tower, battlements and corner turrets at the beginning of the 16th century.

The tower collapsed during a storm in 1779. The interior column was inserted during the Victorian restorations to prevent any further collapse.

In the bottom right hand picture it is possible to make out the two roof indents. The steeper, heavier stone roof was replaced , in the fifteenth century, with a lighter lead one which needed a less aggressive pitch .