London is the capital city of England and the United Kingdom. It has been a major settlement for over two millennia, originally founded by the Romans who named it Londinium. Located on the River Thames, London grew to become the world's largest city from the early 19th century until the 1920s. During this period, London also experienced cholera epidemics in 1848 and 1866 that claimed thousands of lives due to overcrowded conditions.