The History of the Pentagon

What It Covers

The Pentagon, built in 16 months starting September 11, 1941, transformed from a temporary wartime office consolidation for 24,000 scattered War Department personnel into the permanent headquarters of the U.S. Department of Defense and a global symbol of American military power.

Key Questions Answered

• •Structural efficiency: A five-sided, low-rise design across five concentric rings with 10 radial corridors allows any two points in the 6.6 million square foot building to be reached within approximately seven minutes on foot, demonstrating how geometry can solve large-scale logistical challenges.
• •Wartime material constraints: Steel rationing forced engineers to build the Pentagon almost entirely from reinforced concrete, requiring 41,492 concrete piles, 680,000 tons of sand and gravel, and 435,000 cubic yards of concrete — a constraint that later proved life-saving during the 9/11 attack.
• •Proactive security hardening: Post-1995 Oklahoma City bombing renovations added blast-resistant windows, Kevlar wall linings, vehicle crash barriers, and remote delivery inspection facilities. These upgrades, already installed in the west wedge by 2001, directly reduced casualties when Flight 77 struck on 9/11.
• •Institutional permanence through mission expansion: Originally planned as temporary wartime infrastructure, the Pentagon became permanent because Cold War commitments, NATO, nuclear deterrence, and the Korean War prevented postwar military downsizing — a pattern where emergency infrastructure outlasts its original justification by decades.