In 1216 Prince Louis of France laid siege to the Castle.
His men dug tunnels that undermined and brought down the Eastern Tower.
Only the bravery and ferocious fighting of the garrison under Hubert de Burgh saved the castle.

After the siege remedial work was carried out to strengthen this area of the castle.
The main task was to build fortifications to protect the surrounding moat and to
create sally ports from which to attack the enemy forces.

This passage leads from the foot of a spiral staircase inside the castle to St John's Tower which was constructed in the moat.