rights to travel and trade west of that line, and to "bring under your sway the said mainland and islands with their residents and inhabitants and to bring them to the Catholic faith." In 1494 Portugal and Spain signed the Treaty of Tordesillas which moved the line separating their spheres of influence to 300 leagues west of the Cape Verde Islands. The treaty was eventually endorsed by Pope Julius II in the 1506 bull . Throughout the sixteenth century, Spain and Portugal claimed that papal authority had given them exclusive rights of discovery, trade and conquest of non-Christian lands in their respective spheres of influence. These claims were challenged by theorists of natural law such as the Spanish theologians Domingo de Soto and Francisco di Vitoria. In 1539 Vitoria wrote that the Spanish discovery of the Americas provides "no support for possession of these lands, any more than it would if they had discovered us." France and England also disputed the notion that discovery by itself could provide title over lands inhabited by non-Christians. In 1541, French plans to establish colonies in Canada drew protests from Spain. In response, France effectively repudiated the papal bulls and claims based on discovery without possession, the French king stating that "Popes hold spiritual jurisdiction, and it does not lie with them to distribute land amongst kings" and that "passing by and discovering with the eye was not taking possession." Similarly, when in 1580 Spain protested to Elizabeth I about Francis Drake's violation of the Spanish sphere, the English queen replied that popes had no right to grant the world to princes, that she owed no allegiance to the Pope, and that mere symbolic gestures (such as erecting monuments or naming rivers) did not give property rights. From the sixteenth century, France and England asserted a right to explore and colonize any non-Christian territory not under the actual possession of a Christian sovereign. The stated justifications for this included the spread of Christianity, the duty to bring civilization to barbarian peoples, the natural right to explore and trade freely with other peoples, and the right to settle and cultivate uninhabited or uncultivated land. Hugo Grotius, writing in 1625, stated that discovery does not give a right to sovereignty over inhabited land, "For discovery applies to those things which belong to no one." Dutch policy was to acquire land in North America by purchase from