Rome (Latin and Italian: Roma ) is the capital city and a special comune of Italy (named Comune di Roma Capitale). Rome also serves as the capital of the Lazio region. With 2,879,728 residents in 1,285 km (496.1 sq mi), it is also the country's most populated comune. It is the fourth most populous city in the European Union by population within city limits. It is the centre of the Metropolitan City of Rome, which has a population of 4,355,725 residents, thus making it the most populous metropolitan city in Italy. Rome is located in the central-western portion of the Italian Peninsula, within Lazio (Latium), along the shores of the Tiber. Vatican City (the smallest country in the world) is an independent country inside the city boundaries of Rome, the only existing example of a country within a city; for this reason Rome has sometimes been defined as the capital of two states.