Willibrand was at the imperial court in Italy at the time of his election and may have used the opportunity to obtain authorization from the pope for a crusade against the Drenthers. The Papal bull declaring a crusade does not survive; but the "Deeds of the Bishops" indicates that Willibrand received papal authorization for a crusade indulgence. He preached and recruited crusaders in Frisia in the late summer and autumn of 1228, in the summer of 1230 and in the winter of 1230–31. The charge against the Drenthers was almost certainly that they were heretics for defying their bishop's authority ("contemptus clavium", contempt for the keys of the kingdom).