By the year 1283 the order was in possession of all the country between the Vistula and the Memel, Prussia, Courland, part of Livonia, and Samogitia; commanderies were established everywhere to hold it in subjection, and bishoprics and monasteries were founded for the spread of Christianity among the heathen population. In the contests between the Venetians and the Genoese, the Teutonic Knights aided the former, and in 1291, after the loss of Acre, the grand master took up his residence in Venice. About this time the Pope originated a scheme for the union of the three orders of the Hospitalers, the Templars, and the Teutonic Knights, into one great order, purposing at the same time to engage the Emperor and the kings of Christendom to lay aside all their quarrels, and combine their forces for the recovery once for all of the Holy Land. Difficulties without number, which proved insuperable, prevented the realization of this scheme. Among these was the objection raised by the Teutonic Knights, that while the Hospitalers and Templars had but one object in view--the recovery of Palestine, their order had to maintain its conquests in the North of Europe, and to prosecute the spread of the true faith among the still heathen nations. In 1309, when all hope of the recovery of the Christian dominion in the East had been abandoned, and no further crusades seemed probable, it was determined to remove the seat of the grand master from Venice to Marienberg. At a chapter of the order held there, further regulations were agreed upon for the government of the conquered countries, some of which are very curious, but give an interesting picture of the state of the people and of society at that period. Thus it was commanded that no Jew, necromancer, or sorcerer should be allowed to settle in the country. Masters who had slaves, and generally Prussians, prisoners of war, were obliged to send them to the parish church to be instructed by the clergy in the Christian religion. German alone was to be spoken, and the ancient language of the country was forbidden, to prevent the people hatching conspiracies, and to do away with the old idolatry and heathen superstitions. Prussians were not allowed to open shops or taverns, nor to act as surgeons or accoucheurs.