The Spanish Inquisition differed from the older medieval inquisition and from the later Roman Inquisition in one decisive respect: it answered to the Spanish crown rather than to the papacy. Ferdinand and Isabella petitioned Pope Sixtus IV for authority to establish their own tribunal in 1478, and although the pope granted it, the Spanish monarchs retained the power to appoint and remove inquisitors, which made the institution an arm of royal government carried out in the church's name rather than a church body the crown merely hosted.
Its first target was the conversos, families of Jewish or, somewhat later, Muslim descent who had converted to Catholicism, often under considerable pressure, in the decades before 1478. Conversion did not settle the question of loyalty for many Old Christians, who suspected converso families of continuing to practice their former faith in secret, and the Inquisition's procedure, built around denunciation and confession under interrogation, was designed to test exactly that suspicion rather than to police open dissent. Trials were conducted in secret, with the accused often unaware of the specific charge or their accuser's identity, and a formal reconciliation ceremony, the auto-da-fe, publicly announced sentences ranging from penance to, in the rarer and more severe cases, execution by the secular authorities to whom the Inquisition itself handed condemned prisoners.