We're now 64 pictures into Fort Pike, how have we not spent any time with this part of a casemate yet? As originally built, the guns mounted in casemates would have been connected to the embrasure by a tongue that stuck into this opening. All of those cool iron pins we've been seeing slid down into a hole in that tongue, holding the gun's carriage in place and allowing for free movement, with wheels on the rear of the carriage rolling along curved stone (sometimes iron) tracks emplaced in the casemate's floor. In this case we also have lots of mud, because we're right there at the drainage channel opening!