When the Endicott improvements were built at Fort Zachary Taylor in the Florida Keys in 1898, they filled in the top two tiers of casemates on one side of the fort, filling the space with, among other things, the Civil War-era cannon that they were replacing. Obviously something similar happened at Fort Delaware, since here I am walking through the lowest level of casemates under the Endicott battery, but I do have to wonder what they filled those upper casemates in with!? Old guns? Corpses of Spaniards? Sure would be interesting to find out, but for right now I need to concentrate on not touching those bat-infested casemate walls. No, I didn't see any bats while I was there, but they're obviously there. Obviously.