Originally built for the 1962 World's Fair, the Space Needle stands 605 feet tall and, at the time of its completion, was the tallest structure in the U.S. west of the Mississipi River. The architecture of the Space Needle is the result of a compromise between designs of two men, Edward E. Carlson and John Graham, Jr. The two leading ideas for the World Fair involved businessman Edward Carlson's sketch of a giant balloon tethered to the ground (see the gently sloping base) and architect John Graham's concept of a flying saucer (see the halo that houses the restaurant and observation deck). The Space Needle celebrated its 50th anniversary in 2012.