Did Martin Luther actually nail a copy of his 95 Theses to a church door? What do we know and not know about this?
The de.wikipedia has dedicated a whole section to the historicity of this incident. In the introduction:
Die Historizität des Thesenanschlags, bei dem Luther seine 95 Thesen am 31. Oktober 1517 eigenhändig an die Tür der Schlosskirche in Wittenberg genagelt haben soll, ist umstritten.
The historicity of the incident that Luther shall have nailed the 95 theses on the church door in Wittenberg at 31. Oct. 1517 is debatable.
Although in de.wikipedia the article has not properly used citation in situ to reveal the sources of individual sentences. The debatable nature of the theses-nailing is shared by a number of websites, including luther.de:
Daß Luther an besagtem Tag seine Thesen mit lauten Hammerschlägen an die Tür der Schloßkirche zu Wittenberg genagelt haben soll, gehört aber wohl in das Reich der Legenden (Die Legende vom Thesenanschlag).
The incindent that Luther at the said day nailed his theses with loud hammerstrokes on the door of the Schloßkirche in Wittenberg belongs to the realm of legends.
More info comes from Frankfurt Allgemeine:
In the article it wrote that there is no definitive answer to this day. 300 publications have been dedicated to the subject.
First, Luther himself never mentioned the nailing. The whole nailing thing comes from the testimony of Luther's comrade Philipp Melanchthon and a note from Luther's secretary Georg Rörer (this note was rediscovered in 2006 with lots of media coverage). Both refered to one nailing event. The "Pro-nailing" historian believe that two accounts are independent and Rörer's account appearred even in Luther's lifetime. The "Against-nailing" historian asserted that yes, they were from Luther's comrade, but not from the witnesses of the event and what is more, they were penned 20 years after the said days. And they believed the whole thing is to build a myth.
What is sure is that Luther sent his theses to two bishofs at that day and later also to others. Also, the theses were written to provoke a theological discussion about indulgence. It was common in those days to print these theses in Wittenberg. And according to the theology faculty it was also common at those days to paste the prints on church doors. So if Rörer is a reliable source, Luther's theses were also nailed at several churches. So nailing theses at the door was at that time more like an announcement thing rather than a war-declaration.