London is the capital city of both the United Kingdom and the constituent country of England. The ancient City of London to which the name originally belonged still retains its mediaeval boundaries, but the name “London” has long applied more generally to the whole metropolis which has grown up around it. An important settlement for around two millennia, London is today one of the world’s leading business, financial and cultural centres, and its influence in politics, education, entertainment, media, fashion and the arts all contribute to its status as one of the major global cities. London is the most populous city within city limits in the European Union with an official population of 7.5 million and has a metropolitan area population of between 12 and 14 million people. Its diverse population draws from a wide range of peoples, cultures and religions, speaking over 300 different languages. It is an international transport hub, with five international airports and a large port. It serves as the largest aviation hub in the world, and its main airport, the multi-terminal Heathrow, carries more international passengers than any other airport in the world. It also has the World’s largest underground railway system when measured by route length. London is a major tourist destination, with four world heritage sites and numerous iconic landmarks such as the Houses of Parliament, Tower Bridge, the Tower of London, Westminster Abbey, Buckingham Palace and the London Eye among its many attractions, along with famous institutions such as the British Museum and the National Gallery. Its main geographical feature is the River Thames which runs through the city from the south-west to the east.