The tallest building in Seattle is the 76-story Columbia Center, which rises 937 feet (286 m) and was completed in 1985. As the nation has grown so has the U.S. Capitol: today it covers well over 1.5 million square feet, has over 600 rooms, and miles of corridors.The Washington Monument has been the world's tallest stone structure since its completion in 1884, standing 555 feet, 5 inches tall. The Washington Monument is the world's tallest stone structure made from blocks of marble granite and blue stone. There are three buildings in the District of Columbia that are taller: the Basilica, the Old Post Office Pavilion, and the Washington National Cathedral. The Washington Monument is an obelisk on the National Mall in Washington, DC, built to commemorate George Washington, a Founding Father of the United States.