The blockhouse was designed in 1867, originally as a barracks building capable of housing one company of soldiers (about 65 men). Rifle slots or loop holes to shoot from were built into the walls. The designer of the building also designed and built at least two other such structures at other nearby forts (Fort Zarah and Fort Larned). However, both of these structures were hexagonal in design which makes sense from a defensive standpoint as it is nearly a circle having no "blind corners" your enemy could use to approach your position in relative safety. However, "wings" with square corners were added to the Fort Hays structure. From the 20th Century perspective, it was thought the wings were a last-minute addition, put on when it was determined that the fort was safe from attack. But the wings have loop holes as well and from the construction stand point, the wings are integrated into the main section, showing us they were built along with the rest of the building. However, to add to the mystery, it is apparent that the windows in the center section were an afterthought, as they were just cut into the walls after the walls were erected. They have no lintels. But the windows in the wings do have lintels indicating they were built into the walls as the walls were constructed. Numerous other interior design features add to the muddled picture of how and why this building was built. Oh, and by the way, the building was never used for defense (the fort was never attacked) nor was it apparently ever used to house a company of troops. Instead, it was used as the headquarters building, housing office space for the commanding officer and living quarters for the post adjutant.