It is hard to conceive of a greater responsibility than that of a mediæval Inquisitor. The life or death of the heretic was practically at his disposal. The Church, therefore, required him to possess in a pre-eminent degree the qualities of an impartial judge. Bernard Gui, the most experienced Inquisitor of his time (1308-1323), thus paints for us the portrait of the ideal Inquisitor: "He should be diligent and fervent in his zeal for religious truth, for the salvation of souls, and for the destruction of heresy. He should always be calm in times of trial and difficulty, and never give way to outbursts of anger or temper. He should be a brave man, ready to face death if necessary, but while never cowardly running from danger, he should never be foolhardy rushing into it. He should be unmoved by the entreaties or the bribes of those who appear before his tribunal; still he must not harden his heart to the point of refusing to delay or mitigate punishment, as circumstances may require from time to time. "In doubtful cases, he should be very careful not to believe too easily what may appear probable, and yet in reality is false; nor, on the other hand, should he stubbornly refuse to believe what may appear improbable, and yet is frequently true. He should zealously discuss and examine every case, so as to be sure to make a just decision.... Let the love of truth and mercy, the special qualities of every good judge, shine in his countenance, and let his sentences never be prompted by avarice or cruelty."[1] [1] _Practica Inquisitionis_, pars 6a, ed. Douais, 1886, pp. 231-233. This portrait corresponds to the idea that Gregory IX had of the true Inquisitor. In the instructions which he gave to the terrible Conrad of Marburg, October 21, 1223, he took good care to warn him to be prudent as well as zealous: "Punish if you will," he said, "the wicked and perverse, but see that no innocent person suffers a your hands:" _ut puniatur sic temeritas perversorum, quod innocentiæ puritas non lædatur_. Gregory IX cannot be accused of injustice, but he will ever be remembered as the Pope who established the Inquisition as a permanent tribunal, and did his utmost to enforce everywhere the death penalty for heresy.