After the Treasury Department moved from Philadelphia to Washington D. C. in 1800, its headquarters were destroyed by arsonists in 1801, 1814 and 1833. Robert Mills was commissioned to build a fireproof structure. The East and Center Wings were completed in 1842. The South wing was added in 1860 followed by the North Wing in 1869. Those imposing granite, Ionic columns stand 36 feet tall. Free guided tours are available to view this oldest government department building in Washington, D. C.