Under Gregory XI Pierre de Cros was the "most important and powerful courtier" of the pope, and their bedchambers were joined by a secret staircase. Senator
Gui de Prohins, named as military governor of Rome by Gregory XI, was not a party to their intrigues, being loyal to the Pope. Pierre de Cros also controlled the
Apostolic Camera (established 1361), the judicial wing of the Camera, which had "absolute and final" jurisdiction over any case affecting the interests of the Camera, even if already pending in front of other
ecclesiastical courts, and even if they involved issues of theology. This court was not burdened by the
ordo iudiciarius, the slow and formalistic rules of the papal courts, but rather gave expedited and summary rulings. It was in no small part due to the unwillingness of Murat to coerce the extreme taxation ordered by Gregory XI, that the pontiff found himself bankrupt by his wars against the
Visconti and ultimately by the
War of the Eight Saints, fought against a coalition of Italy city states led by the
Republic of Florence, which instigated rebellion in the
Papal States. While Gregory XI was forced to borrow from the
Duke of Anjou, Murat excelled at diplomacy, convincing Bologna to relent in exchange for a lifting of the
interdict. De Cros drafted and persuaded his cousin Gregory XI to adopt
Futuris peculis on 19 March, modifying the laws of the
papal conclave. He also persuaded Gregory XI to make
Pierre Rostaing, the
castellan of
Castel Sant'Angelo to swear not to turn over the fortress to any papal claimant without the assent of the six cardinals remaining in the
Comtat Venaissin. Fearing for his own life, he moved into the fortress and prepared it for a long siege. Rather than guarding the conclave personally (as he would later do at
Fondi), Murat de Cros deputized the
Bishop of Valence and Die to perform the task.
During the Western Schism during the
Papal Conclave of 1378. De Cros did not accept the election of Prignano as Urban VI, and sheltered in Castel Sant'Angelo a group of like-minded cardinals, which included his brother. He met the
bardaresi, carrying a battleaxe and followed by a heavily armed entourage, refusing to allow him to escort the cardinals back for a
papal coronation ("That fool thinks he’s pope? I surely don’t consider him pope"). Later in the day Murat de Cros and the other cardinals went to pay homage to Urban VI although he feigned illness to avoid the coronation. He carried on his duties as chamberlain as if Gregory XI were still in power and Urban VI did not exist, refusing to date his letters according to the latter's election. As Chamberlain of the Camera (Camerlengo), de Cros held a curial office which was one of the few that did not expire during a
sede vacante, as established by the bull
Ubi periculum (1274). He persuaded the entire College of Cardinals to convene in
Anagni, himself leaving Castel Sant'Angelo between 25 June and 1 July. He issued a formal summons to Prignano to appear before a cameral tribunal in Anagni, and sometime before 10 July declared him excommunicated and deprived of his Archbishopric of Bari. Also under the judicial power of the Apostolic Camera, Murat de Cros received the cardinals on 2 August, and after hearing accounts of the conclave, declared it null and void and the church to continue in
sede vacante. This meeting was neither a consistory or a conclave but a tribunal with Murat de Cros presiding as an ordinary judge. De Cros worked to arrange a meeting of the
College of Cardinals at
Fondi on 20 September 1378 which elected
Robert of Geneva as Clement VII. According to Williman, "de Cros used his huge discretionary powers to make himself virtually a regent or protector, a keeper of the papal power
sede vacante". It was at this point that Murat de Cros appointed a new procurator and registrar for the Camera, and assisted Clement VII in turning out copious amounts of official-looking documents. ==Cardinal==