"Fort Knox" means two different things that sit side by side in north-central Kentucky, about 35 miles southwest of Louisville. The first is a U.S. Army post that began as a World War I training camp in 1918. The second is the United States Bullion Depository, a granite vault built on land taken from the post in 1936, where the Treasury keeps about half of the nation's gold.

The Army post is named for Henry Knox, George Washington's chief of artillery in the Revolutionary War and the first Secretary of War. In the 1930s it became the home of the Army's mechanized cavalry, and in 1940 it became the headquarters of the new Armored Force, the organization that built the tank divisions of World War II. For decades afterward it was the Army's Armor Center, the school for tank crews, and a key part of American military history.

The Bullion Depository is run by the U.S. Mint, part of the Department of the Treasury, and guarded by the U.S. Mint Police. It holds 147,341,858.382 fine troy ounces of gold, according to the Mint. No visitors are allowed, and only a few outside groups have ever seen inside the vault.

Fort Knox's fame goes beyond soldiers and gold. During World War II the depository protected the Declaration of Independence and the Constitution. The name became shorthand for anything heavily guarded ("as safe as Fort Knox"), and it has appeared in films such as the 1964 James Bond movie Goldfinger. Today the post is headquarters for the Army's personnel, recruiting, and ROTC commands and hosts the Army's largest yearly training event.