The Washington Monument is a large, white obelisk made of marble, granite, and sandstone in the middle of the National Mall.  Construction began in 1848 and finished in 1884. Upon completion it became the tallest structure in the world at 555 ft 5 1/8 in.  The cap is made of aluminum, which at the time was a rare metal and had the same value as silver.  It is still the tallest building in Washington, D.C. due to a law made in 1910 restricting new buildings’ height to be no more than 20 feet greater than the width of the street they are on. There is a common misconception that the law states that no building can be taller than the Washington Monument, but the law makes no mention of this.  More than 800,000 visitors a year ride the elevator to the top of the monument.  In 1983 the monument was “held hostage” by a nuclear arms protester named Norman Mayer, claiming to have explosives in his van parked next to the monument. After 10 hours of deliberations, and all 8 hostages being set free, Mayer was shot and killed by park police. Afterwards police discovered that his van did not contain explosives.  On July 15th, 2005 a $15 million dollar security and renovation project was completed that improved the grounds and now makes it impossible for anyone to drive up to the monument.