Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in 1,285.3 km (496.3 sq mi). In 2006 the population of the metropolitan area was estimated by the Organisation for Economic Co-operation and Development to have a population of 3.7 million. The city of Rome is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.