In 1219, trial by jury replaces trial by ordeal to adjudicate criminal liability. The lack of reasons given to sustain the jury’s verdict mirrors the practice of the ordeal (also called God’s judgment) and endures to this day in common law countries such as England, the U.S. or Canada, despite an ongoing controversy. Our thesis here is that we can learn much about this “black box” practice through perusing the historical continuity between these two forms of trial, the new and the old. How does trial by jury relate to trial by water (or by fire)? Procedural similarities are striking. Both represent the dramatization of a public “ordeal”; both rely on proceedings attuned to the interests of the parties instead of those of an all-powerful State; both imply a certain role for the judge in terms of the construction of the truth, and the nature of this truth. But how do these similarities help explaining why the truth of the verdict continues to be today what it has always been: without given reasons and very difficult to upset through an appeal? In other words, what we explore here is how the rise and fall of the medieval judgment of God can contribute to a better understanding of the modern institution of the jury in England and Canada, including the lack of reasons still characterizing its verdicts.