Justice, medieval style

"The ordeal system worked surprisingly well. It accurately determined who was guilty and who was innocent, sorting genuine criminals from those who had been wrongly accused. Stranger still, the ordeal system suggests that pervasive superstition can be good for society. Medieval legal systems leveraged citizens’ superstitious beliefs through ordeals, making it possible to secure criminal justice where it would have otherwise been impossible to do so. Some superstitions, at least, may evolve and persist for a good reason: They help us accomplish goals we couldn’t otherwise accomplish, or accomplish them more cheaply.
First, consider the reasoning of the defendants. Guilty believers expected God to reveal their guilt by harming them in the ordeal. They anticipated being boiled and convicted. Innocent believers, meanwhile, expected God to protect them in the ordeal. They anticipated escaping unscathed, and being exonerated.
The only defendants who would have been willing to go through with the ordeal were therefore the innocent ones. Guilty defendants would have preferred to avoid the ordeal - by confessing their crimes, settling with their accusers, or fleeing the realm"
read article by Peter Leeson
Justice, medieval style - The Boston Globe