London

London is the capital and most populous city in the English-speaking country of the United Kingdom. It is located on the River Thames in south-east England, at the head of an estuary that stretches for 50 miles (80 kilometres) and empties into the North Sea. For more than two millennia, London has been a significant settlement. Londinium was the name given by the Romans to the City of London, which served as the city's historic core and financial centre. The Square Mile, as it is known informally, maintains borders that are very similar to those of the mediaeval city. The national government has been based in the nearby City of Westminster for hundreds of years. North and south of the Thames, there are 31 more boroughs in London. The Mayor of London and the London Assembly are in charge of the administration of the London area.

London is a big worldwide city and one of the most populous in the world. It has a significant impact on the arts, commerce, education, entertainment, fashion, finance, health care, the media, professional services, research and development, tourism, and transportation, among other areas of activity. With a gross domestic product (GDP) of €801.66 billion in 2017, London is the most prosperous city in Europe. It is one of the world's biggest financial centres, and in 2019, it had the second highest number of ultra-high-net-worth people in Europe, behind Paris, according to the World Wealth Report. In 2020, London had the second-highest number of billionaires of any European city, behind only Moscow in terms of total wealth. The universities of London constitute the greatest concentration of higher education institutions in Europe. Imperial College London, which specialises in scientific and applied sciences, the London School of Economics, which specialises in social sciences, and the comprehensive University College London are among the top-ranked universities in the city. In 2012, London became the first city in modern history to hold three Summer Olympic Games, a distinction previously held by just one other city.

More than 300 languages are spoken in London, thanks to the city's varied population and cultural mix. It has a population of about 9 million people in mid-2018 (equivalent to Greater London), making it the third-most populated metropolis in Europe. One in every four people in the United Kingdom lives in London. With a population of 9,787,426 people in the 2011 census, the Greater London Built-up Area is the fourth most populated in Europe, behind only Istanbul, Moscow, and Paris. With 14,040,163 people in 2016, the London metropolitan region ranks third in terms of population in Europe, behind behind Istanbul and the Moscow Metropolitan Area.

In addition to the Tower of London and Kew Gardens, London also boasts the Palace of Westminster, which includes Westminster Abbey and St Margaret's Church, as well as Greenwich, which is home to the Royal Observatory, Greenwich, which is responsible for establishing the Prime Meridian (0° longitude) and Greenwich Mean Time. Buckingham Palace, the London Eye, Piccadilly Circus, St Paul's Cathedral, Tower Bridge, Trafalgar Square, and The Shard are among the other notable monuments. Museums, galleries, libraries, and sports events abound in London, as do cultural institutions. The British Museum, the National Gallery, the Natural History Museum, the Tate Modern, the British Library, and the West End theatres are among the institutions on this list. Because it was built in 1863, the London Underground is the world's first mass-transit system.