This article studies the text and context of an unedited seventeenth century copy of the famous bull Vergentis in Senium of Pope Innocent III, which he sent in 1203, during the reign of Peter the Catholic, to Queen Sancha of Aragon, widow of Alfonso the Troubadour. The letter was sent in response to a petition for advice from Sancha as to how to proceed against heretics found in the crown of Aragon. These heretics were most probably Waldensians in High Aragón. This letter, sent as it was at a moment of great historical importance (on the eve of the coronation of Peter II in Rome) gives us new clues to the relationship between the Arago-Catalan monarchy and the papacy concerning the problem of heresy.This article studies the text and context of an unedited seventeenth century copy of the famous bull Vergentis in Senium of Pope Innocent III, which he sent in 1203, during the reign of Peter the Catholic, to Queen Sancha of Aragon, widow of Alfonso the Troubadour. The letter was sent in response to a petition for advice from Sancha as to how to proceed against heretics found in the crown of Aragon. These heretics were most probably Waldensians in High Aragón. This letter, sent as it was at a moment of great historical importance (on the eve of the coronation of Peter II in Rome) gives us new clues to the relationship between the Arago-Catalan monarchy and the papacy concerning the problem of heresy