But Pepin had hardly recrossed the Alps on his way home, when Aistulf again advanced against Rome, and lay siege. The pope summoned Pepin to fulfill anew his pledge of loyalty. In 756 Pepin set out with an army against Aistulf and again hemmed him in at Pavia. Aistulf was again compelled to promise to the pope the cities granted him after the first war and, in addition, Commachio at the mouth of the Po. But this time a promise was not sufficient. Pepin's messengers visited the various cities of the exarchate and of the Pentapolis, demanded and received the keys to them, and brought the highest magistrates and most distinguished magnates of these cities to Rome. Pepin executed a new deed of gift for the cities thus surrendered to the pope, and laid it with the keys of the cities on the grave of St. Peter in the Second Donation of 756.