On this day in 1941, several months ahead of the United States’ entry into World War II, the War Department broke ground on its new headquarters, called the Pentagon. The generals demanded an HQ with four million square feet of office space—twice as much as the Empire State Building—that was big enough to hold 40,000 people, with parking for 10,000 cars. One catch, though: it could be no more than four stories high because a) they wanted to protect views of DC; and b) anything taller would require too much steel. And steel was then urgently needed for battleships and weapons to be used in a war we weren’t quite fighting yet.
Anyway, the first site engineers chose, set below the Lee Mansion, was an odd, five-sided plot of land, hence the building’s design. But even four stories were going to block views there, so they moved a mile downriver to an area known as Hell’s Bottom. New location, but they kept the same old pentagonal design.
Then, on this day exactly sixty years later, five al Qaeda hijackers seized American Airlines Flight 77, which had departed Dulles International Airport at 8:20 that morning en route to Los Angeles. At 9:37 a.m. the Boeing 757 was flown into the first floor of the Pentagon’s west wall at a speed of approximately 460 knots. All of the plane’s fifty-eight passengers and crew, as well as the hijackers, died instantly.
The Washington Post lists the victims of the Pentagon attack here.
Finally, on this day in 2008, a memorial designed for the site was dedicated. It covers the two-acre site along the plane’s path to the building with trees and 184 benches built atop small reflecting pools, each representing a victim.
A version of this post was originally published on September 11, 2011.
IMAGES: September 11 (Miguel Ángel Ovejero Aranda); the Pentagon under construction in a photograph that appeared in the May 1943 issue of LIFE (Myron Davis); the Pentagon as it appeared after the terrorist attack on September 11, 2001.