London is the capital of and largest city in England and the United Kingdom, with the largest municipal population in the European Union. London has been a major settlement for two millennia. Londinium was founded by the Romans. The City of London, London's ancient core and colloquially known as the Square Mile − retains boundaries that follow closely its medieval limits. The City of Westminster is also an Inner London borough holding city status. Greater London is governed by the Mayor of London and the London Assembly.
London is considered to be one of the world's most important global cities and has been termed the world's most powerful, most desirable, most influential, most visited, most expensive, innovative, sustainable, most investment friendly, most popular for work, and the most vegetarian-friendly city in the world. London exerts a considerable impact upon the arts, commerce, education, entertainment, fashion, finance, healthcare, media, professional services, research and development, tourism and transportation. London ranks 26 out of 300 major cities for economic performance. It is one of the largest financial centres and has either the fifth or sixth largest metropolitan area GDP. It is the most-visited city as measured by international arrivals and has the busiest city airport system as measured by passenger traffic. It is the leading investment destination, hosting more international retailers and ultra high-net-worth individuals than any other city. London's universities form the largest concentration of higher education institutes in Europe. In 2012, London became the first city to have hosted three modern Summer Olympic Games. London contains four World Heritage Sites: the Tower of London; Kew Gardens; the site comprising the Palace of Westminster, Westminster Abbey, and St Margaret's Church; and the historic settlement in Greenwich where the Royal Observatory, Greenwich defines the Prime Meridian, 0° longitude, and Greenwich Mean Time. Other landmarks include Buckingham Palace, the London Eye, Piccadilly Circus, St Paul's Cathedral, Tower Bridge, Trafalgar Square and The Shard. London has numerous museums, galleries, libraries and sporting events. These include the British Museum, National Gallery, Natural History Museum, Tate Modern, British Library and West End theatres. The London Underground is the oldest underground railway network in the world. London is one of the major classical and popular music capitals of the world and hosts major music corporations, such as Universal Music Group International and Warner Music Group, as well as countless bands, musicians and industry professionals. The city is also home to many orchestras and concert halls, such as the Barbican Arts Centre (principal base of the London Symphony Orchestra and the London Symphony Chorus), Cadogan Hall (Royal Philharmonic Orchestra) and the Royal Albert Hall (The Proms). London's two main opera houses are the Royal Opera House and the London Coliseum. The UK's largest pipe organ is at the Royal Albert Hall. Other significant instruments are at the cathedrals and major churches. Several conservatoires are within the city: Royal Academy of Music, Royal College of Music, Guildhall School of Music and Drama and Trinity Laban.