The main gate of Fort Clinch! Originally one crossed the glacis and entered the fort over a Swing Bridge, which pivoted at its center. Perhaps this was intended to twirl at a high rate of speed with attackers on it, causing them to get dizzy, vomit, and then be too embarassed to continue the attack. This twirly bridge concept was also employed at fellow Polygonal Fort Fort Montgomery, at Rouses Point, New York.

One doubts that Fort Clinch's bridge can still pivot. In fact, I have yet to experience a fort whose original drawbridge system is still operational, because really, why would such be maintained? A drawbridge or twirlybridge would have been an enormously difficult thing to keep in working order, maintenance that must have seemed particularly unnecessary when attack seemed unlikely.