 Christians, he said, must not slacken in following Christ on account of such false assurances.According to Philipp Melanchthon, writing in 1546, Luther nailed a copy of the "Ninety-five Theses" to the door of the Castle Church in Wittenberg that same day — church doors acting as the bulletin boards of his time — an event now seen as sparking the Protestant Reformation, and celebrated each year on 31 October as Reformation Day.Some scholars have questioned the accuracy of Melanchthon's account, noting that no contemporaneous evidence exists for it.