colony of Castel di Castro. Some of the fortifications that still surround the current district of Castello were built by the Pisans, including the two remaining white limestone towers (early 14th century) designed by the architect Giovanni Capula. Together with the district of Castello, Castel di Castro comprised the districts of Marina (which included the port), and later and Villanova. Marina and Stampace were guarded by walls, in contrast to Villanova, which was mostly home to peasants. 14th to 17th centuries In the second decade of the 14th century the Crown of Aragon conquered Sardinia after a series of battles against the Pisans. During the siege of Castel di Castro (1324-1326), the Aragonese, led by Alfonso IV of Aragon, built a stronghold on a more southern hill, that of Bonaria. When the fortified city was finally conquered by the Aragonese army, Castel di Castro (Castel de Càller or simply Càller in Catalan) became the administrative capital of the newborn Kingdom of Sardinia, one of the many kingdoms forming the Crown of Aragon, which later came under the rule of the Spanish Empire. After the expulsion of the Tuscans, the Castello district was repopulated by the Aragonese settlers of Bonaria while the indigenous population was, as in the past, concentrated in Stampace and Villanova. The kings of Sardinia, also kings of Aragon and later kings of Spain, were represented in Cagliari by a viceroy, who resided in the Palazzo Regio. In the 16th century the fortifications of the city were strengthened with the construction of the bastions and the rights and benefits of the Aragonese were extended to all citizens. The intellectual life was relatively lively and in the early years of the 17th century the university was founded. 18th century In 1718, after a brief rule by the Habsburgs, Cagliari and Sardinia came under the House of Savoy. As rulers of Sardinia, the Savoys took the title of kings of the Sardinian kingdom. During the Savoyard Era, until 1848, the institutions of the Sardinian kingdom remained unchanged, but with the "Perfect Fusion" in that year, all the possessions of the House of Savoy House, comprising Savoy, Nice (now part of France), Piedmont and from 1815 Liguria, were merged into a unitary state. Although Sardinian by name, the kingdom had its parliament in Turin, where the Savoys resided, and its members were mainly aristocrats from Piedmont or the mainland. In the