Gregory IX fully understood the help that the Dominicans and Franciscans could render him as agents of the Inquisition throughout Christendom.
It is probable that, the Senator of Rome refers to them in his oath in 1231, when he speaks of the _Inquisitores datos ab Ecclesia_.[1] Frederic II, in his law of 1232, also mentions the _Inquisitores ab apostolica sede datos.[2] The Dominican Albéric traveled through Lombardy in November, 1232, with the title of _Inquisitor hereticæ pravitatis.[3] In 1231 a similar commission was entrusted to the Dominicans of Freisach and to the famous Conrad of Marburg. Finally, to quote but one more instance, Gregory IX, in 1233, wrote an eloquent letter to the bishops of southern France in which he said: "We, seeing you engrossed in the whirlwind of cares, and scarce able to breathe in the pressure of overwhelming anxieties, think it well to divide your burdens, that they may be more easily borne. We have therefore determined to send preaching friars against the heretics of France and the adjoining provinces, and we beg, warn, and exhort you, ordering you, as you reverence the Holy See, to receive them kindly, and to treat them well, giving them in this as in all else, favor, counsel, and aid, that they may fulfill their office."
[1] Raynaldi, _Annales_, ad ann. 1231, sect. 16, 17.
[2] Cap. iii, in the _Mon. Germ., Leges_, sect. iv, vol. ii, p. 196.
[3] Potthast, _Regesta Roman. Pontif_., no. 904, 1.
Their duties are outlined in a letter of Gregory IX to Conrad of Marburg, October 11, 1231: "When you arrive in a city, summon the bishops, clergy and people, and preach a solemn sermon on faith; then select certain men of good repute to help you in trying the heretics and suspects denounced before your tribunal. All who on examination are found guilty or suspected of heresy must promise to absolutely obey the commands of the Church; if they refuse, you must prosecute them, according to the statutes which we have recently promulgated." We have in these instructions all the procedure of the Inquisition: the time of grace; the call for witnesses and their testimony; the Interrogation of the Accused; the reconciliation of repentant heretics; the condemnation of obdurate heretics.