Introduction to the Old Post Office: This building is the famous old post office built in 1873. It was the location of the U.S. Postal Service, Customs House and U.S. Court Hall. The architectural style is the same as the Louvre Museum in Paris, and it is the second largest post office in the world. Imperial period architectural style. Today, there are only two buildings from the Second Empire era in the United States. The St. Louis Old Post Office is one of them, and the other is the Old Executive Office Building (OEOB), the staff office of the White House in Washington, DC.