Frederick's son Henry VI actually managed to extend Hohenstaufen authority in Italy by his conquest of the Norman Kingdom of Sicily, which comprised Sicily and all of Southern Italy. Henry's son, Frederick II, Holy Roman Emperor – the first emperor since the 10th century to actually base himself in Italy – attempted to return to his father's task of restoring imperial authority in the northern Italian Kingdom, which led to fierce opposition not only from a reformed Lombard League, but also from the Popes, who had become increasingly jealous of their temporal realm in central Italy (theoretically a part of the Empire), and concerned about the hegemonic ambitions of the Hohenstaufen emperors.