designs of L'Enfant. The Commandant's House exemplifies Greek Revival architecture, rare on Army installations in the United States. The army also built the six cavelike casemates as defensive structures in the case of an enemy siege during the reconstruction of 1798–1801. Soldiers used a "bake oven" just inside the main gate and the entrance to the bomb-proof casemate for baking bread, as a chapel, and as a mess hall. The army designed the largest casemate (#1) as a barracks. The three smaller casemates were used for storage. The architects intended Casemate #5, about half the size of Casemate #1, as the headquarters of Fort Mifflin in the time of attack. The army built the blacksmith shop before 1802; it is probably the oldest surviving complete structure at Fort Mifflin. In 1814, a two-story officers' quarters, measuring by , was built. In the 1811 annual report of the secretary of war, Fort Mifflin was described as "...mounting 29 heavy guns, with a water battery without (outside) the works, mounting 8 heavy guns... with brick barracks for 100; within 3/4 of a mile... (is) the Lazaretto, which are good barracks for 400 men." Pre-Civil War period The U.S. Army built a one-story brick structure, by , in 1815–1816 as a guardhouse and prison. Around 1819, north of the walls of the fort, the army also built a building used as a hospital (2nd floor) and mess hall (ground floor). After the construction of Fort Delaware in 1820, Fort Mifflin was relegated to secondary status. During the 19th century the area around the fort was drained and filled until Mud Island connected with the western bank of the Delaware River. Nevertheless, the building and garrisoning of Fort Mifflin continued. In the early 1820s, the army began meteorological observations at the fort. The soldiers' barracks building was extensively renovated in 1836, along with the officers' quarters. At a later date the soldiers' barracks was again renovated, at which time the roofline was changed to add the second floor. (HABS # PA-1225E). In 1837 the hospital and mess hall building was converted to a meetinghouse and an artillery shed, for the storage and protection of cannon, was built on an interior raised platform. By 1839, the army designated the one-story brick guardhouse-prison as an arsenal. On 27 December 1842 the army completed a brick, one-story sutler building/storehouse measuring by . In the 1840s a two-story