This is the South Casemate Battery, which was intended to mount a series of 24-pounder guns in defense of Fort Niagara's main gate: It's fire would interlock with that from the North Casemate Gallery. Affairs betwixt the United States and Great Britain had calmed down by 1872, and guns were never mounted within these casemates...until the fort was restored for historical purposes from 1926 to 1934, and guns like this 24-pounder Flank Howitzer were placed herein.