The earliest fortification on this site was a Saxon burh (fortified settlement) from c. 1000 which consisted of a rectangular earthen banked enclosure with a later stone facing. This was modified into a Motte & Bailey castle c. 1100-1135 under Henry I.
In the 13th century Countess Isabella de Fortibus modified the stone castle defences into the form we see today adding a great hall with a chamber and chapel at either end and courtyard buildings.
Elizabeth I appointed George Carey as Captain of the island in 1583. He modified the courtyard buildings again and added a new range to the great hall. Due to the potential for Spanish invasion Carey converted the outer defences into a modern artillery fort between 1587 and 1602 with the addition of 5 angular bastions and other smaller alterations.
During the Civil War the castle was in the hands of Parliament and became a prison for Royalists including King Charles I 1647-8.
LiDAR data from Environment Agency Geomatics
Model created with Planlauf TERRAIN