Efforts towards the Protestant Reformation began before 1517. But, the start of revolutionary movement is most associated with that year and Martin Luther's nailing of his 95 Thesis to the University of Wittenberg's chapel door. Luther's disenchantment with the Catholic Church had been mounting for years. Finally, when Pope Leo X endorsed the selling of a new wave of indulgences to fund the building of St. Peter's Basilica, the incensed Augustinian monk "protested" by listing 95 points on which he felt the Church was in error. When his university superiors and fellow faculty failed to respond, he sought the opinions of friends in other places who had the document published both in it's original Latin and in a German translation.
Photo credit: Martin Luther’s 95 Theses in the original Latin, a printing from the early 1500s, epchurch.net
Read the thesis in English:
A Sampling of Influential Older Titles