According to The Pentagon: The First 50 Years, a book by our chief historian, Alfred Goldberg, here is what the architects thought: Casey and Bergstrom and their associates recognized that a building of the proposed proportions would require a great deal of ground and an efficient design that would permit ready access on foot to all parts of the structure. Casey recollected that Bergstrom probably deserved the greatest credit for the pentagonal design. Other layouts — square, rectangular and octagonal — were considered, and the group finally settled on the pentagonal. Luther Leisenring pointed out later that the idea of a five-sided building was not new. Many old forts were of pentagonal shape, and the notion of a building shaped like a fortress may well have influenced the planners.