The States of the Church were in a certain sense the only remnant of the Roman Empire in the West which escaped foreign conquerors. Gratefully the Roman population acknowledged that they had escaped subjection to the Lombards. Also, temporal sovereignty guaranteed to the pope some level of independence. Under Pepin's son, Charlemagne, relations with the Lombards became strained again. Adrian I complained that the Lombard king Desiderius had invaded the territories of the States of the Church, and reminded Charlemagne of the promise made at Quiercy. As Desiderius also championed the claims of Charlemagne's nephews, he endangered the unity of the Frankish kingdom, and Charlemagne's own interests therefore bade him to oppose Desiderius. In the autumn of 773 Charlemagne entered Italy and besieged Desiderius at Pavia. While the siege was in progress, Charlemagne went to Rome at Easter, 774, and at the request of the pope renewed the promises made at Quiercy.