Union Square is an 11-acre public plaza at the foot of Capitol Hill in Washington, D.C., USA. It encompasses the Ulysses S. Grant Memorial (1924) and the 6-acre Capitol Reflecting Pool (1971) and is just west of the United States Capitol building. Views differ as to whether the Square is just east of the National Mall or is itself the eastern end. Interstate 395 transits the Third Street Tunnel just beneath Union Square.