Rome 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. The city has been a major human settlement for over two millennia. With 2,879,728 residents in 1285 km2, it is also the country's most populated comune. It is the third 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 second or third most populous metropolitan city in Italy depending on definition. 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.