Sardinia world (22 centenarians/100,000 inhabitants). Sardinia is the first discovered Blue Zone, a demographic and/or geographic area in the world with an oversize concentration of centenarians and supercentenarians. In 2016 there were 50,346 foreign national residents, forming 3% of the total Sardinian population. The most represented nationalities were: Sardinia's most populated cities are Cagliari and Sassari. The Metropolitan City of Cagliari has 431,302 inhabitants, or about ¼ of the population of the entire island. Eurostat has identified in Sardinia two Functional Urban Areas: Cagliari, with 477,000 inhabitants, and Sassari, with 222,000 inhabitants. Sardinia is one of the five Italian autonomous regions,
Kingdom of Sardinia of the Duchy of Milan, while Charles VI (the Holy Roman Emperor and Archduke of Austria), received the Spanish Netherlands, the Kingdom of Naples, Sardinia, and the bulk of the Duchy of Milan. During the War of the Quadruple Alliance, Victor Amadeus II, Duke of Savoy and Prince of Piedmont, had to agree to yield Sicily to the Austrian Habsburgs and receive Sardinia in exchange. The exchange was formally ratified in the Treaty of The Hague of 17 February 1720. Because the kingdom of Sardinia had existed since the 14th century, the exchange allowed Victor Amadeus to retain the title