The medieval bishops of Sion were generally appointed from the younger sons of noble families of Savoy and Valais and often drew the resources of the see into the feuds of these families. Moreover, the bishops were vigorously opposed, as a matter of principle, by the petty feudal nobles of Valais, each in their fortified castle on rocky heights, seeking to evade the supremacy of the bishop who was at the same time count and prefect of the Holy Roman Empire. Especially in the 14th and 15th centuries, the benefactors in these traditional struggles were often the rich peasant communities of Upper Valais, which were called later the "Sieben Zehnden" (the "seven tithings"), who exacted increasing political rights as the price of support, beginning with the success of the rebellion of 1415–1420.