Notwithstanding the failure of this first enterprise, Boniface left England again in 718 and for ever; and now went through France to Rome to obtain papal sanction for his future missionary work. Pope Gregory II. formally commissioned him as missionary to the German tribes (719). Armed with that letter and many precious relics, he started north the following spring to his field of labour. First, he went to Thuringia and Bavaria, regions already partly Christianised, but at this time considerably disorganised, and demanded their submission to Rome; then, learning of King Radbod's death (719), he hastened to Frisia, where he laboured for three years with Willibrord, who had meantime returned to continue his labours. In 722 he passed through Thuringia and entered Hesse where, within a short time, he converted two local chiefs together with many thousands of their followers. A foothold was thus secured by Rome in the pagan world of Germany and never again lost. These successes led the Pope to recall Boniface to Rome to receive directions concerning conditions in Germany. After exacting from him a confession of faith in the Trinity, and binding him by an oath ever to respect papal authority,[246:1] the Supreme Pontiff created him missionary bishop in 723. Boniface then returned to Germany with a code of laws for the Church, and with letters of introduction to Charles Martel and to other influential persons who might aid him. He was aware that little could be done without the assistance of that powerful ruler and wrote: "Without the protection of the Prince of the Franks, I could neither rule the people of the Church, nor defend the priests or clerks, the monks or handmaidens of God; nor have I the power to restrain pagan rites and idolatry in Germany without his mandate and the awe of his name."[246:2] Hence he attached himself for awhile to the court of the Frankish ruler before he began the work so near his heart. Hesse and Thuringia, Christianised nominally by Celtic missionaries and consequently under no episcopal authority, refused to recognise papal jurisdiction. To awe them into submission, Boniface cut down their gigantic sacred oak at Geismar and from it, subsequently, built a chapel to St. Peter. The people were convinced and received the new faith. With the aid of Charles Martel, the assistance of the pope, and the help of English missionaries who joined him, Boniface completed his conquest of that region, filled it with churches and monasteries, and extended papal rule over it. Schools were established, learning and a higher civilisation began to flow in from England and Rome, and the dark days of paganism were gone.