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,
Sardinia Kingdom ended and Sardinia was returned to Roman rule. In 533, Sardinia returned to the rule of the Byzantine Empire when the Vandals were defeated by the armies of Justinian I under the General Belisarius in the Battle of Tricamarum, in their African kingdom; Belisarius sent his general Cyril to Sardinia to retake the island. Sardinia remained in Byzantine hands for the next 300 years aside from a short period in which it was invaded by the Ostrogoths in 551. Under Byzantine rule, the island was divided into districts called "mereíai" (μερείαι) in Byzantine Greek, which were governed by a