The Republic of San Marino is an enclaved microstate surrounded by Italy, on the north-eastern side of the Apennine Mountains. Its size is just over 61 km2 (24 sq mi) with an estimated population of over 30,000. Its capital is the City of San Marino. San Marino has the smallest population of all the members of the Council of Europe. San Marino claims to be the oldest surviving sovereign state and constitutional republic in the world, as the continuation of the monastic community founded on 3 September 301, by stonecutter Marinus of Arba. Legend has it that Marinus left Rab, then the Roman colony of Arba, in 257 when the future emperor, Diocletian, issued a decree calling for the reconstruction of the city walls of Rimini, which had been destroyed by Liburnian pirates.