Washington is the capital city of the United States. The capital of the United States of America was founded in 1791 in the District of Columbia. It is located on the north bank of the Potomac River. Washington, District of Columbia, was named after George Washington and Christopher Columbus. The city is divided into four sections: NW, NE, SW, and SE. Numbered streets run north and south: First Street, Second Street ... Lettered streets such as A-street, B-street run east and west. It has little industry, and only one million people. One reason Washington looks different from other cities is that no building in the city may be more than 40 metres tall. There are no skyscrapers, because they would hide the city's many monuments from view. The White House has been the home of every president with the exception of George Washington White House consists of 132 rooms and tourists may visit only portions of the ground floor and first floor. The White House grounds are open to the public only once a year for the annual Egg Roll held on Easter Monday. Monuments to three presidents - George Washington, Thomas Jefferson and Abraham Lincoln - are among the most popular sights in the city. They stand in a vast green triangular area. The Capitol is one of Washington's most magnificent buildings. It is constructed of white stone and marble and crowned by an impressive dome. On top of the dome stands a bronze Statue of Freedom. Washington's museums and art galleries are among the finest in the world. The Smithsonian Institution consists of museums of similar units in the areas of science, technology, history and art. Several of its museums are on the Mall. The Smithsonian's best-known scientific bodies include the National Museum of Natural History and the National Air and Space museum. The Washington Cathedral is on Massachusetts Avenue, and the Arlington National Cemetery is outside the city limits just across the Potomac River near the Pentagon in Virginia. The famous Tomb of the Unknown Soldier is visited by millions of people every year.