The largest entrance and most heavily defended approach to Fort Warren was the main sallyport. The original design included a drawbridge & portcullis, and interior slope. The current bridge design dates from World War II. The narrow windows on either side allowed defending soldiers to fire onto attackers. The protruding iron rods fastening the inner, yellow oak doors deterred attempts at breaking through with an axe.
Fortify Your Vocabulary
Sallyport: the main entrance to a fort.
Portcullis: a wooden or iron grated fence that impedes travel.