The document that Martin Luther nailed to the door of the Castle Church in Wittenberg, Germany, on October 31, 1517, is known as the "Ninety-Five Theses." The theses were a list of propositions or statements critical of certain practices and teachings of the Roman Catholic Church, particularly concerning the concept of indulgences. The posting of these theses is often considered to mark the beginning of the Protestant Reformation, a major movement that led to the formation of various Protestant denominations and sparked significant religious, political, and social changes in Europe.