In the mid 12th century, Bishop Roger of Salisbury founded the stone outer curtain wall of the castle, it was utilised to protect the medieval town, which occupied much of the Iron Age earthwork. The wall was constructed on the perimeter of the hillfort but was left incomplete on the north-east quadrant. Encased by a huge outer ditch, with its counterscarp bank, the wall wasn't given any flanking towers and was only pierced by the east and west gateways. At the site of the cathedral, beyond the cloister is the only fragment of wall, which stands above the ground.
