By the tenth century the traffic Peter cursed had become the operating system of the Western church. Proprietary churches were bought and sold with their altars; German and French kings invested bishops with ring and staff and expected payment or service; the papacy itself was, at low moments, an object of family purchase. The reform that answered began at Cluny and radicalized in Rome, and under Gregory VII, from 1073, simony stood beside clerical marriage as one of the two named diseases the Gregorian reform existed to cure.
The reformers' argument sharpened doctrine: some, like Cardinal Humbert, held simoniacal ordinations simply void, sacraments bought being no sacraments, a position the church eventually softened, but the polemical energy came from the older equation, that selling the sacred is heresy against its nature as gift. Because the sale of offices was inseparable from lay control of appointments, the campaign against simony widened inevitably into the Investiture Controversy, the struggle over whether emperors could install bishops at all, with its excommunications, its Canossa and its compromise at Worms in 1122, which conceded canonical election while kings kept the temporalities. Simony was never abolished, only chased inward and upward; late medieval fee schedules, dispensations and the indulgence traffic kept the substance alive under better bookkeeping, and the Reformers made the charge general. The canon law of every subsequent century has restated the prohibition, testimony less to victory than to the permanence of the temptation wherever spiritual office carries worldly goods.