Auricular confession, the practice of privately confessing sins to a priest, made mandatory in 1215.
The engine reads it as an unmatched early intelligence system for understanding what people were thinking and doing.
Because everyone confessed privately to priests, the Church effectively mapped the inner lives of the whole European population. The secrecy is protected by the 'seal of confession,' overseen by a Vatican office, though it's now under pressure from mandatory-reporting laws.
It shows how a religious ritual doubled as a vast information network, and that network is now being strained by modern legal duties to report crimes.