The event where Martin Luther challenged the Catholic Church is known as the Ninety-Five Theses, which he famously nailed to the Wittenberg Castle Church door in 1517. In this document, Luther criticized the Church's practice of selling indulgences and called for reforms in Catholic doctrine and practices, emphasizing salvation through faith alone. This act is often regarded as the catalyst for the Protestant Reformation, leading to the emergence of various Protestant denominations and significant changes in religious and political landscapes throughout Europe. Luther’s challenge sparked widespread debate and ultimately transformed the course of Western Christianity.