In the 10th century, possession passed to the Holy Roman Emperor Otto the Great. The earliest fortifications still standing today date from this period. The first urban structures that eventually became the modern city of Bellinzona rose on the eastern side of the fortified hill in the 12th century. The conflict in Italy between partisans of the Holy Roman Emperor, the Ghibellines) and the partisans of the Pope, the Guelfs, was mirrored in Bellinzona. The second of the three castles, Montebello, was added to the defensive system by the Ghibelline Rusca family near the end of the 13th century. Bellinzona fell to the Visconti, Dukes of Milan, in 1340. The strategic importance of Bellinzona increased further in the 15th and 16th centuries when the opposing powers fought to expand their respective territorial dominance. The suzerainty of Milan, under its new overlords the Sforza, was resisted by the rest of Italy, forcing the city to strengthen its defenses. As its stronghold in the north, Bellinzona also had to be fortified anew, at great expenses, with the building of the city walls and a thirds castle at Sasso Corbaro. Following the defeat of the Dukes of Milan, Bellinzona sought the protection of the Swiss Confederation in the year 1500. King Louis XII of France, who had ended the Milanese suzerainty, reluctantly ceded Bellinzona in 1503 to the three cantons of Uri, Schwyz and Unterwald, founders of the Swiss Confederation.