The Pentagon was initially planned to be on land that was bordered by five side roads, which led architects to design a five-sided building. However, U.S. President Roosevelt thought the initial location would obstruct the view of Washinton from Arlington Cemetary, so he chose to move it to its present location while maintaining the unique five sides.

Exactly 60 years before the terrorist attacks on September 11, 2001, builders broke ground for the Pentagon on September 11, 1941.

In 2001, the Pentagon was undergoing renovations that were divided into the five wedges of the building. On September 11, 2001, when American Airlines Flight 77 flew into the Pentagon and killed 189 people, the plane hit wedge 3, where renovations were just completed. 4,500 people normally work in this area, but only 800 people were there due to the renovations.

Col. Leslie Groves was an Army Corps of Engineers officer and was in charge of the Pentagon’s construction in 1941. He worked six days of the week in Washington and would visit a project that needed his personal attention on Sundays. He was assigned to direct the Manhattan Project, America’s endeavor to build an atomic bomb.

Did you know the Pentagon is the world’s largest low-rise office building? In fact, the entire U.S. Capitol building could fit inside the Pentagon. The building is 6,500,000 square feet of office space, which is three times the floor space of the Empire State Building.

Col. Leslie Groves was known as an intimidating and demanding boss. His deputy, Army Maj. Robert Furman was assigned to be at the Pentagon all day and night, staying at the building for days without going home to refuel. To help him catch up on sleep, Furman had the Pentagon’s contractors construct a secret apartment in what would become the Army’s Ordnance Divison.

A few of Groves’ other deputies would catch up on their sleep here, shower, and head back to the job. Furman used the apartment on official trips back to Washington when he served as an intelligence officer on the Manhattan Project. But, in 1943, he was snoozing when ordnance officers found him and told him to leave the apartment.