 Frederick could only take possession of the lands north of the Danube, because Rudolf of Rheinfelden's son, Berthold, asserted his authority over the southern parts of Swabia.Henry met with the papal legates, Bishops Peter of Albano and Udalric of Padua, in Regensburg on 12 May 1079.They convinced him to send envoys to Fritzlar to begin negotiations with Rudolf of Rheinfelden with their mediation.