Bristol is a city, ceremonial county and unitary authority in England. On the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. It is in the West of England Combined Authority and the most populous city in South West England. The wider Bristol Built-up Area is the eleventh most populous urban area in the United Kingdom. Iron Age hillforts and Roman villas were built near the confluence of the rivers Frome and Avon.