Philip's father-in-law George, Duke of Saxony, the bishop of Würzburg, Konrad II von Thungen, and the archbishop of Mainz, Albert III of Brandenburg, were active in agitating against the growth of the Reformation. Their activities, along with other circumstances, including rumors of war, convinced Philip of the existence of a secret league among the Roman Catholic princes. His suspicions were confirmed to his own satisfaction by a forgery given him by an adventurer who had been employed in important missions by George of Saxony, one Otto von Pack. After meeting with Elector John of Saxony in Weimar on 9 March 1528, it was agreed that the Protestant princes should take the offensive in order to protect their territories from invasion and capture.