 The low roof of these magazines forms a banquette or fire step so that the garrison could fire their muskets over the parapet in the event of an infantry attack.The parapet is also pierced by the main gate, which was originally the only access to the redoubt.The redoubt is surrounded by a ditch or dry moat which is 30 feet (9 metres) from the top of the parapet and 25 feet (7 metres) wide.