In medieval communities where everyone shared similar faith in God’s omniscience and justice, the guilty were less willing to undergo a “trial by ordeal,” because the innocent could expect God to protect them. The priests in charge of administering a “trial by ordeal” would prepare the boiling water or hot iron in advance, in private; they could go easy on the fuel if they felt the circumstances merited mercy, and in public they could stretch out their prayers, thereby leaving more time for the heat to dissipate, and thus helping to facilitate the miraculous protection of the innocent.

Of course I’d prefer a fact-based trial by jury, but in an age before forensic science, the guilty were incentivized to admit their guilt, and take a lesser punishment, rather than risk burning their hand, thereby being sentenced to a more severe punishment (on top of the self-inflicted injury).

There’s just one hitch: while only an innocent defendant will choose to undergo the ordeal, which allows the court to learn that he’s in fact innocent, when he sticks his hand in the boiling water, it burns him, declaring his guilt! To deliver justice, however, the court needs to do more than simply learn that an innocent defendant is innocent – it needs to find him so.

How could an ordeal-administering priest make boiling water innocuous to an innocent defendant’s flesh? By making sure that it wasn’t actually boiling.

The ‘instruction manuals’ for administering ordeals that medieval European priests followed provided them ample opportunity to do just that. The fire used to heat the water was prepared by the priest in private, permitting him to cool the fire. The priest ‘sprinkled’ holy water over the water in the ordeal cauldron, permitting him to cool the water. The ordeal cauldron was removed from the fire at a point during the mass, and the defendant wasn’t tested until the priest was done praying, allowing him to cool the water some more by drawing out his prayers. And ordeal observers were placed at a respectable distance from the ordeal ‘stage’, enabling the priest to carry out his manipulations undetected. Did I mention that it was the priest who adjudged the ordeal’s final outcome – whether the defendant’s hand had indeed been burned? —Aeon