During its original construction, the walls of the Church were never completed, however, the 1771 inventory describes them as being at least as high as the spring line of the stone vault ribs, which were described as being in place. The 1849 Captain Seth Eastman drawing depicts the east, apse wall of the building as somewhat lower than the other walls. A ramp of earth was piled against the inside of this wall in order to place a cannon at that location.
When the U.S. Army occupied the site as a quartermaster's depot, the walls were made level all around in order to accommodate the installation of a roof. At this time, stones were added to the facade to bring the walls on each side of the center section up to level, and to raise the height of the center section to receive the gable end of the roof. Since the west end of the roof was hipped (i.e. it sloped down to meet the wall), not requiring this treatment, one must assume that there was more than a practical reason for this modification. The profile of the building, as a result of this rounded cresting, has become an iconic symbol of the quest for freedom. The Army also added windows along the north, east, and south walls.
When the Army occupation roof was replaced with a concrete barrel vault in 1921, sections of concrete with a rough pebble surface were added to the tops of the walls to create parapets.