On this date in 1941, ground was broken for the Pentagon Building in Arlington, Virginia. In July of that year, Brigadier General and engineer Brehon B. Somervell had summoned two of his subordinates and told them to draw up plans for an office building to house 40,000 War Department workers; it should be four stories tall, he told them, and cover 4 million square feet. He gave them their assignment on Thursday afternoon, and said he wanted the plans on his desk by Monday. They delivered, and construction began two months later. Sixteen months later, the Pentagon was complete.
Sixty years to the day after the groundbreaking, on September 11, 2001, a passenger jet piloted by terrorist hijackers crashed into the Pentagon, killing all aboard the jet and more than a hundred people inside the building itself. The jet crashed into a wing that was being remodeled, so many of the offices were unoccupied; otherwise, the death toll would have been much higher.