Rome (Italian: Roma) is the capital city of Italy and of the Lazio region, as well as the country's largest and most populous comune, with more than 2.7 million residents. The metropolitan area has a population of about 4 million. It is located in the central-western portion of the Italian peninsula, where the river Aniene joins the Tiber. The Mayor of Rome is Walter Veltroni. An enclave of Rome is the State of the Vatican City, the sovereign territory of the Holy See. It is the smallest nation in the world, and the capital of the only religion to have representation in the United Nations (as a non-member observer state). Rome, Caput mundi ("capital of the world"), la Città Eterna ("the Eternal City"), Limen Apostolorum ("threshold of the Apostles"), la città dei sette colli ("the city of the seven hills") or simply l'Urbe ("the City"), is thoroughly modern and cosmopolitan. As one of the few major European cities that escaped World War II relatively unscathed, central Rome remains essentially Renaissance and Baroque in character. The Historic Centre of Rome is listed by UNESCO as a World Heritage Site.