In some places Boniface found a strange mixture of heathen superstitions with Christianity, and he did all that he could to root them out. He had also much trouble with missionaries from Ireland, whose notions of Christian doctrine and practice differed in some things from his; and perhaps he did not always treat them with so much of wisdom and gentleness as might have been wished. But after all he was right in thinking that the sight of more than one kind of Christian religion, different from each other and opposed to each other, must puzzle the heathen and hinder their conversion; so that we can understand his jealousy of those Irish missionaries, even if we cannot wholly approve of it. In reward of his labours and success, Boniface was made an archbishop by Pope Gregory III. in 732; and, although at first he was not fixed in any one place, he soon brought the German Church into such a state of order that it seemed to be time for choosing some city as the seat of its chief bishop, just as the chief bishop of England was settled at Canterbury. Boniface himself wished to fix himself at Cologne; but at that very time the bishop of Mentz got into trouble by killing a Saxon, who, in a former war, had killed the bishop's father. Although it had been quite a common thing in those rough days for bishops to take a part in fighting, Boniface and his councils had made rules forbidding such things, as unbecoming the ministers of peace; and the case of the bishop of Mentz, coming just after those rules had been made, could not well be passed over. The bishop, therefore, was obliged to give up his see; and Mentz was chosen to be the place where Boniface should be fixed as archbishop and primate of Germany, having under him five bishops, and all the nations which had received the Gospel through his preaching. When Boniface had grown old, he felt himself again drawn to Frisia, where, as we have seen,[64] he had laboured in his early life; and at the age of seventy-five he left his archbishopric, with all that invited him to spend his last days there in quiet and honour, that he might once more go forth as a missionary to the barbarous Frieslanders. Among them he preached with much success; but on Whitsun eve, 755, while he was expecting a great number of his converts to meet, that they might receive confirmation from him, he and his companions were attacked by an armed party of heathens, and the whole of the missionaries, fifty-two in number, were martyred. But although Boniface thus ended his active and useful life by martyrdom at the hands of those whom he wished to bring into the way of salvation, his work was carried on by other missionaries, and the conversion of the Frisians was completed within no long time. Boniface's body was carried up the Rhine, and was buried at Fulda, a monastery which he had founded amidst the loneliness of a vast forest; and there the tomb of the "Apostle of the Germans" was visited with reverence for centuries.