1517 AD
On October 31, 1517, Martin Luther, an Augustinian monk and theology professor at the University of Wittenberg, posted his 95 Theses on the door of the Castle Church. His target was the sale of indulgencesβpayments to the Church that promised to reduce punishment for sinsβbut his theses also challenged the authority of the Pope and the very nature of salvation.
Luther's theses were quickly translated into German and spread throughout Europe thanks to the printing press. What began as an academic debate escalated into a full-blown theological and political revolution. In 1521, Luther was excommunicated by Pope Leo X and declared an outlaw by Emperor Charles V at the Diet of Worms. His famous declaration, 'Here I stand, I can do no other,' became the rallying cry of the Reformation.
The Reformation would fracture Western Christianity into dozens of denominations and ignite decades of religious warfare across Europe. Key Sources: Luther's 95 Theses; Diet of Worms transcript; Pope Leo X's Exsurge Domine; Diarmaid MacCulloch, A History of Christianity