The Washington Monument is an obelisk on the National Mall in Washington, D.C., built to commemorate George Washington, once commander-in-chief of the early Continental Army and the first American president.
The monument, made of marble, granite, and bluestone gneiss, is both the world's tallest stone structure and the world's tallest obelisk, standing 555 feet 5 1⁄8 inches (169.294 m) tall. Taller monumental columns exist, but they are neither all stone nor true obelisks.
Construction of the monument began in 1848, was halted from 1854 to 1877, and was finally completed in 1884. The hiatus in construction happened because of co-option by the Know Nothing party, a lack of funds, and the intervention of the American Civil War. A difference in shading of the marble, visible approximately 150 feet (46 m) or 27% up, shows where construction was halted. Its original design was by Robert Mills, an architect of the 1840s, but his design was modified significantly when construction resumed. The cornerstone was laid on July 4, 1848; the capstone was set on December 6, 1884, and the completed monument was dedicated on February 21, 1885. It officially opened October 9, 1888. Upon completion, it became the world's tallest structure, a title previously held by the Cologne Cathedral. The monument held this designation until 1889, when the Eiffel Tower was completed in Paris, France... Source