Lateran Council With Constantine's supporters largely dealt with, Stephen wrote to the
Frankish king,
Pepin the Short, notifying him of his election, and asking for a number of bishops to participate in a council he was seeking to hold to discuss the recent confusion. As Pepin had died, it was
Charlemagne and
Carloman I who agreed to send twelve bishops to participate in the
Lateran Council of 769. The council saw the final condemnation of Constantine II, who was beaten and had his tongue removed before being returned to his monastic cell. All clerical appointments made by Constantine were declared null and void. It also set about establishing strict rules for papal elections, thereby restricting the involvement of the nobility in subsequent elections. Finally, the rulings of the
Council of Hieria were rejected, and the practice of devotion to
icons was confirmed (see
iconoclasm). In 770, Stephen was asked to confirm the election of Michael, a
layperson, as
archbishop of Ravenna. In fact, Michael, in league with the Lombard king
Desiderius and the duke of
Rimini, had imprisoned
Leo I, who had been elected first. Stephen refused to confirm Michael's election; citing the conventions of the Lateran council, he sent letters and envoys to Michael, demanding that he stand down. Michael refused, and the stand-off continued for over a year, until the arrival of the Frankish ambassador in Ravenna along with the
papal legates encouraged Michael's opponents to overthrow him, and send him to Rome in chains. Leo followed soon after, when Stephen consecrated him as archbishop. Placing his hope in the Franks, he attempted to mediate in the quarrels between
Charlemagne and
Carloman I, Pepin's sons and successors, which were only helping the Lombards' cause in Italy. In 769, he helped them reconcile, and pressured them to support the still infant Papal States, by reminding them of the support that their father had given the
papacy in the past. He also begged them to intercede on his behalf by entering into discussions with the Lombards. Consequently, an embassy was sent to the Lombard king, Desiderius, in 770, which included Charlemagne's mother,
Bertrada of Laon. Their intervention achieved a result favourable to the papacy by restoring to the pope the parts of
Benevento that the popes claimed. It is also possible that discussions took place around the marriage of Charlemagne's sister,
Gisela to Desiderius' son,
Adalgis. Stephen therefore wrote to both Charlemagne and Carloman, protesting about the proposed alliance. Apart from noting that both men were already married, he reminded them of their promises to previous popes, that they would consider the pope's enemies as their enemies, and that they had promised to
Saint Peter to resist the Lombards and restore the rights of the Church. He wrote: "You who are already, by the will of God and the commands of your father, lawfully married to noble wives of your own nation, whom you are bound to cherish. And certainly it is not lawful for you to put away the wives you have and marry others, or ally yourselves in marriage with a foreign people, a thing never done by any of your ancestors.... It is wicked of you even to entertain the thought of marrying again when you are already married. You ought not to act thus, who profess to follow the law of God, and punish others to prevent men acting in this unlawful manner. Such things do the heathen. But they ought not to be done by you who are Christians, a holy people and a kingly priesthood." Stephen's pleas fell on deaf ears, and Charlemagne married Desiderata in 770, temporarily cementing a familial alliance with the Lombards.
Fall of Christophorus and Sergius Throughout 769 and 770, Stephen continued to rely on the support and advice of Christophorus and Sergius who had placed him on the papal throne. Their antipathy towards the Lombards and general pro-Frankish stance caused King Desiderius to engineer their downfall. He bribed the
Papal Chamberlain, Paulus Afiarta, and other members of the papal court to spread rumors about them to the pope. By this stage, Stephen had returned to the Lateran, and he was confronted in the Basilica of St. Theodore by the fleeing Afiarta and his co-conspirators being chased by Christophorus and his supporters. Apparently at this point, a suspicious Christophorus, believing that Stephen had entered into some agreement with Desiderius, forced Stephen into taking an oath that he would not turn Christophorus or his son over to the Lombards. After this, a furious Stephen berated Christophorus, demanded he stop harassing Afiarta, and ordered him and his followers to withdraw, to which Christophorus complied. The Lombard king, shutting Stephen up in his suites in the Basilica, made it clear to the Pope that the price for his help was to be the handing over of Christophorus and Sergius. The Pope sent two bishops to negotiate with Christophorus and Sergius, telling them that they must either retire to a monastery or come out to him at St. Peter's. At the same time, a message was sent from Desiderius to the people of the city, declaring that: "Pope Stephen bids you not to fight against your brethren, but to expel Christophorus from the city, and save it, yourselves, and your children." This message from the Lombard king had the desired effect; Christophorus and Sergius began to suspect their associates, who in turn rapidly abandoned them. Both were reluctant to leave the city, but eventually both made their way to the Pope during the night. The next day Stephen was allowed to return to the city, while Christophorus and Sergius were left in Lombard hands. Negotiations to secure their release were unsuccessful, and before the day was out, Afiarta arrived with his partisans. After discussing the situation with Desiderius, they had both men blinded. Christophorus died after three days, while Sergius was kept in a cell in the Lateran. wherein he declared that Christophorus and Sergius had been involved in a plot with an envoy of Charlemagne's brother, Carloman, to kill the Pope. Further, that Stephen had fled to Desiderius for protection, and that eventually Christophorus and Sergius were brought out against their will. While Stephen managed to save their lives, later a group of men had them blinded, but not on Stephen's orders. He then concludes that if it wasn't for "his most excellent son Desiderius", he would have been in fatal danger, and that Desiderius had reached an agreement with him to restore to the Church all the lands that she had claims on that were still in Lombard hands. That such a letter was a fiction was demonstrated very soon after; when Stephen asked Desiderius to fulfil the promises he had made over the body of
Saint Peter, the Lombard king responded: "Be content that I removed Christophorus and Sergius, who were ruling you, out of your way, and ask not for rights. Besides, if I do not continue to help you, great trouble will befall you. For Carloman, king of the Franks, is the friend of Christophorus and Sergius, and will be wishful to come to Rome and seize you."
Continuing troubles and the death of Stephen Desiderius continued to stir trouble in Italy; in 771, he managed to convince the bishops of
Istria to reject the authority of the
Patriarch of Grado, and to have them place themselves under the
Patriarch of Aquileia, which was directly under Lombard control. Stephen wrote to the rebellious bishops, suspending them and ordering them to place themselves once again under the authority of Grado, or face
excommunication. Then on 24 January, eight days before Stephen's death, Afiarta dragged the blinded Sergius from his cell in the Lateran and had him strangled. or 1 February 772. He was succeeded by
Adrian I. ==Local cult of sainthood==