The United States Bullion Depository, often known as Fort Knox, is a fortified vault building located within the United States Army post of Fort Knox, Kentucky, used to store a large portion of United States official gold reserves and occasionally other precious items belonging or entrusted to the federal government. The exact contents of the United States Bullion Depository are unknown as there has not been an approved full audit since the early 1930s, before the Depository's construction. It is estimated to have roughly 3 percent of all the gold ever refined throughout human history.