The beginning of the Protestant Reformation is typically marked by the legendary event on October 31, 1517, when the German monk Martin Luther nailed his "Ninety-Five Theses" to the door of the Castle Church in Wittenberg. These theses challenged the Catholic Church's practices, particularly the sale of indulgences, and called for reform. Luther's actions and writings ignited a religious revolution, leading to widespread dissent and the eventual formation of Protestantism as a separate branch of Christianity. This event, known as the "95 Theses," is regarded as the catalyst for the Protestant Reformation, fundamentally altering the course of European religious history.