William wrote that stories of supposed revenants were a "warning to posterity" and so common that, "were I to write down all the instances of this kind which I have ascertained to have befallen in our times, the undertaking would be beyond measure laborious and troublesome." According to William, "It would not be easy to believe that the corpses of the dead should sally (I know not by what agency) from their graves, and should wander about to the terror or destruction of the living, and again return to the tomb, which of its own accord spontaneously opened to receive them, did not frequent examples, occurring in our own times, suffice to establish this fact, to the truth of which there is abundant testimony."