Standing on the River Thames in south eastern England, London, the capital of England and the United Kingdom, is a 21st-century city with history extending back to Roman occasions. At its middle stand the overwhelming Houses of Parliament, the famous ‘Big Ben’ clock tower and Westminster Abbey, site of British monarch coronations, the Tower of London, the notable settlement in Greenwich where the Royal Observatory, Greenwich characterizes the Prime Meridian, 0° longitude, and Greenwich Mean Time, Tower Bridge.