By law the tallest structure in Washington, D.C., the Washington Monument stands 555 feet 5.125 inches in height. There are 897 steps to the top, but an electric elevator brings visitors all the way up in seventy seconds (free tickets are required). Marble taken from Maryland was used in building the monument, but only 153 feet were completed before the Civil War and lack of funding brought construction to a half for 25 years. When it resumed, a marble slightly different in tone was used, causing a noticeable ring around the structure.

Source: http://www.tourmobile.com/sites-stops/washmon.html