In 751 Pippin III, Mayor of the Palace under the Merovingian king, himself assumed the title of king and was anointed by the Church. Pope Stephen II bestowed him the hereditary title of "Patricius Romanorum" as protector of Rome and St. Peter in response to the Donation of Pepin, that guaranteed the sovereignty of the Papal States. Charles the Great (who ruled the Franks from 774 to 814) launched a decades-long military campaign against the Franks' heathen rivals, the Saxons and the Avars. The campaigns and insurrections of the Saxon Wars lasted from 772 to 804. The Franks eventually overwhelmed the Saxons and Avars, forcibly converted the people to Christianity, and annexed their lands to the Carolingian Empire.