London is a city.
Londinium . During the later decades of the 1st century , Londinium expanded rapidly , becoming Great Britain 's largest city . London . It was founded by the Romans , who named it Londinium . 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 . A metropolis ( [ mᵻˈtrɒpəlɪs , _ - plɪs ] ) is a large city or conurbation which is a significant economic , political , and cultural center for a country or region , and an important hub for regional or international connections , commerce , and communications .