The UK capital city that began as the Roman settlement of Londinium was London.
Londinium was established by the Romans on the north bank of the River Thames shortly after the invasion of Britain in AD 43, probably around AD 47–50. The site was strategically valuable: the Thames was narrow enough for a bridge but deep enough for seagoing vessels, making the settlement both a road junction and a major port.
Londinium expanded rapidly and became the commercial centre of Roman Britain. The Iceni revolt led by Boudica destroyed much of the settlement around AD 60 or 61, but the Romans rebuilt it. By the second century, the city had a forum, basilica, amphitheatre, temples, baths, and a population estimated at tens of thousands.
The modern City of London broadly occupies the core of the Roman settlement, although today’s London is vastly larger. Londinium should not be confused with Lundenwic, the later Anglo-Saxon trading settlement that developed west of the abandoned Roman walls.