Gregory IX establishes the Papal Inquisition; converts who have returned to Judaism now fall under the tribunal of faith

Gregory IX gave the pontifical Inquisition, born in Rome against the Cathars of the South, jurisdiction over Jewish affairs: not over Jews as such, who did not fall under the Christian faith, but over converts who had returned to Judaism and over those who received them.

The distinction seems slight; it was fraught with consequences. It made baptism, even received under compulsion, an indissoluble bond whose rupture became a capital crime, and it placed the inner life of communities under the surveillance of a tribunal that could prosecute without complaint and judge without appeal.