Should attackers reach the fort it is surrounded by a deep dry ditch to
prevent any direct attack upon the fort walls.
The main defence of this ditch is from the Firing Steps, which are hidden
from view of an enemy standing on the opposite side of the ditch.
The defenders could load their muskets safely protected by the walls, step
up onto the firing steps, shoot and then step down to reload, their place
being taken by another defender
