Robert Mills (1781-1855), American architect and engineer, born in Charleston, South Carolina. He studied with the English-trained American architect Benjamin H. Latrobe and subsequently practiced as one of the first native professional American architects in Washington, D.C., Philadelphia, and Baltimore, Maryland. In 1820 Mills became state architect and engineer of South Carolina. From 1836 until 1851 he was the official architect of public buildings for the U.S. government. An exponent of the Greek Revival style, Mills achieved simple, finely proportioned, and monumental effects in his work. One of his best-known designs is the Washington Monument, begun in 1848 but not completed until 1884. He also designed the Treasury Building (1836) and the Patent Office Building (1836), now housing the National Collection of Fine Arts and the National Portrait Gallery, in Washington, D.C.