Martin Luther's critique of the Catholic Church, expressed in his famous 95 theses promulgated in 1517, is usually regarded as the opening act of the Protestant Reformation, a religious movement that swept much of northern Europe and Britain in the sixteenth and seventeenth centuries. Luther, himself a monk and professor at Wittenberg University, mainly took issue with the Church's practice, current at the time, of selling indulgences, or forgiveness for sins. This practice, which was viewed as corrupt by many in the Church (Luther was not its only critic) summed up for Luther the ways in which the Church had deviated from its pastoral mission and its Scriptural foundations. Luther argued that salvation could only be achieved through faith, not deeds (i.e. the purchase of indulgences.) This was a serious critique, and it quickly spread throughout the Holy Roman Empire due to the printing press and the fact that some German princes saw political benefits to supporting and protecting Luther. While the movement had many different facets and went in many different directions politically and spiritually, Luther more than any other person is associated with its origins and its character.