London is the capital and most populous city of England and the United Kingdom. Standing on the River Thames in the south east of the island of Great Britain, London has been a major settlement for two millennia. It was founded by the Romans, who named it Londinium. London's ancient core, the City of London, largely retains its 1.12-square-mile (2.9 km2) medieval boundaries. Since at least the 19th century, "London" has also referred to the metropolis around this core, historically split between Middlesex, Essex, Surrey, Kent, and Hertfordshire, which today largely makes up Greater London, governed by the Mayor of London and the London Assembly. London is a leading global city in the arts, commerce, education, entertainment, fashion, finance, healthcare, media, professional services, research and development, tourism, and transportation. It is crowned as the world's largest financial centre and has the fifth- or sixth-largest metropolitan area GDP in the world. London is a world cultural capital. It is the world's most-visited city as measured by international arrivals and has the world's largest city airport system measured by passenger traffic. London is the world's 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 the modern Summer Olympic Games three times.
London has a diverse range of people and cultures, and more than 300 languages are spoken in the region. Its estimated mid-2015 municipal population (corresponding to Greater London) was 8,673,713, the largest of any city in the European Union, and accounting for 12.5% of the UK population. London's urban area is the second most populous in the EU, after Paris, with 9,787,426 inhabitants at the 2011 census. The city's metropolitan area is the most populous in the EU with 13,879,757 inhabitants, while the Greater London Authority states the population of the city-region (covering a large part of the south east) as 22.7 million. The city-region therefore has a similar land area and population to that of the New York metropolitan area. London was the world's most populous city from around 1831 to 1925.
Policing in Greater London, with the exception of the City of London, is provided by the Metropolitan Police Service, overseen by the Mayor through the Mayor's Office for Policing and Crime (MOPAC). The City of London has its own police force – the City of London Police. The British Transport Police are responsible for police services on National Rail, London Underground, Docklands Light Railway and Tramlink services. A fourth police force in London, the Ministry of Defence Police, do not generally become involved with policing the general public.
Crime rates vary widely by area, ranging from parts with serious issues to parts considered very safe. Today crime figures are made available nationally at Local Authority and Ward level. In 2015 there were 118 homicides, a 25.5% increase over 2014. The Metropolitan Police have made detailed crime figures, broken down by category at borough and ward level, available on their website since 2000.
Within London, both the City of London and the City of Westminster have city status and both the City of London and the remainder of Greater London are counties for the purposes of lieutenancies. The area of Greater London has incorporated areas that are part of the historic counties of Middlesex, Kent, Surrey, Essex and Hertfordshire. London's status as the capital of England, and later the United Kingdom, has never been granted or confirmed officially—by statute or in written form.
Its position was formed through constitutional convention, making its status as de facto capital a part of the UK's unwritten constitution. The capital of England was moved to London from Winchester as the Palace of Westminster developed in the 12th and 13th centuries to become the permanent location of the royal court, and thus the political capital of the nation. More recently, Greater London has been defined as a region of England and in this context is known as London.