London, city, capital of the United Kingdom. It is among the oldest of the world’s great cities—its history spanning nearly two millennia—and one of the most cosmopolitan. By far Britain’s largest metropolis, it is also the country’s economic, transportation, and cultural center. Stretching back to Roman times. At its center stand the imposing Houses of Parliament, the iconic ‘Big Ben’ clock tower, and Westminster Abbey, the site of British monarch coronations. Across the Thames River, the London Eye observation wheel provides panoramic views of the South Bank cultural complex and the entire city.