The Principality saw a prosperous period during the 13th century and the first half of the 14th. The population increased; Catalan language and culture expanded into the islands of the Western Mediterranean. The reign of Peter III of Aragon ("the Great") included the conquest of Sicily and the successful defense against a French crusade; his son and successor Alfonso III ("the Generous") conquered Menorca; and Peter's second son James II conquered Sardinia; Catalonia was the center of the empire, expanding and organizing it, establishing institutional systems similar to its own. Barcelona, then the most frequent royal residence, was consolidated as the administrative center of the domains with the establishment of the Royal Archives in 1318. The Catalan Company, mercenaries led by Roger de Flor and formed by Almogavar veterans of the War of the Sicilian Vespers, were hired by the Byzantine Empire to fought the Turks, defeating them in several battles. After the assassination of Roger de Flor by orders of the emperor's son Michael Palaiologos (1305), the Company took revenge sacking Byzantine territory, and they conquered the duchies of Athens and Neopatras in the name of the King of Aragon. Catalan rule over Greek lands lasted until 1390.