On his homeward journey the king heard of the death of the great archbishop of Mainz, the apostle of Transrhenane Germany. Zealous even in extreme old age for the conversion of every subject of the Frankish realm, Boniface had started on a missionary journey to East Friesland, where paganism still held sway. As he lay encamped at Dokkum a great multitude of wild heathen, indignant at the invasion of their last retreat, fell upon him and slew him with all his companions. [Sidenote: Martyrdom of St. Boniface.] His death was not long unavenged; the Christian majority of the Frisians took arms, put down their pagan brethren, slew many thousands of them and compelled the rest to submit to baptism. By his martyr-death the great archbishop completed the conversion of the land for which he had striven so much during his lifetime. He was buried at Fulda in Hesse, where a great abbey was reared over his shrine and became the centre of Christian life in the Hessian lands whose apostle he had been. It would have afforded the keenest pleasure to Boniface if he could have witnessed the zeal with which his patron Pippin went forward with the task of reducing the Frankish clergy to canonical discipline. In the year which followed his martyrdom the Synod of Verneuil passed the most stringent laws against evil-living, simony, the practice of secular avocations, and the other failings of the clergy against which the archbishop had raged in his lifetime. The easy promises which king Aistulf had made when he was beleaguered in Pavia had never been intended for keeping. When the Franks had withdrawn from Italy the king found pretexts for delay, and did not restore to Stephen II. a single one of the Sabine or Latin cities which he had occupied in 753, still less the Exarchate of Ravenna, which the Pope had impudently asked and fondly hoped to receive. [Sidenote: Aistulf attacks Rome.] In the winter of 755-6 he took still more unmistakeable steps of hostility; descending the valley of the Tiber he suddenly laid siege to Rome. The walls of Aurelian were still too strong to be stormed, but three months of blockade brought the citizens near to yielding. The news that king Pippin had once more taken arms restored courage to Pope and people, and ere long Aistulf was forced to raise the siege and hasten north to defend Lombardy. Once more the Franks forced the defiles of the Cenis, and cut to pieces a Lombard force which strove to stop the way. For the second time Aistulf was forced into Pavia, beleaguered, and compelled to sue for peace. This time he was given harder terms. Pippin demanded one-third of the royal hoard of the Lombards, an annual tribute, a larger body of hostages, and the instant surrender of the Exarchate. The unwilling Lombard was forced to concede everything; Frankish envoys received and handed over to the Pope, the cities of Ravenna, Rimini, Pesaro, Forli, Urbino, and Sinigaglia, with all their dependencies.