A Duchy of Naples had been created after the fall of the Exarchate of Ravenna.

Although Naples' Greco-Roman culture endures, it eventually switches allegiance from Constantinople to Rome under Duke Stephen II, putting it under papal suzerainty by 763.

At the beginning of his reign, Naples was still a loyal dukedom of the Empire, her dukes appointed by the emperor.

In 761, therefore, she had denied entry to the papal envoy, the Bishop Paul, an opponent of the iconoclasm then gripping the Eastern Roman world.

Stephen was no less a supporter of the iconoclasm than the emperor himself.

At that time, Stephen had addressed Antiochos, the patrician of Sicily and his technical overlord, as "our lord" and "most excellent patrikios and protostrategos" (763).

By 764, however, Naples had thrown off iconoclasm and Paul is able to take up his see.

Pope Stephen III, having largely dealt with Constantine’s supporters, had written 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 has died, it is Charlemagne and Carloman I who agree to send twelve bishops to participate in the Lateran Council, opened by Stephen in April 769, of which a major topic for discussion is the elevation of Constantine.

The blind Constantine is brought before the council, where they question his elevation to the Apostolic See when he was still a layman.

Constantine responds that he had been forced to take on the role, as the Roman people had been looking for someone to fix the problems left behind by Pope Paul.

He then confesses to the charges, and throws himself on the mercy of the synod.

On the following day however, he retracts his confession, arguing that his actions had not been any different to other papal elections in the past.

He states: ”I have done nothing, my brethren, which cannot be excused by recent examples.

Sergius, a layman like myself, has been consecrated metropolitan of Ravenna; the layman Stephen has even been ordained Bishop of Naples...” Infuriated by his arguments, the synod orders Constantine to be beaten and his tongue torn out, before he is excommunicated from the Church.

Constantine’s acts and rulings are then publicly burnt before the entire synod.

He is returned to his monastery, after which nothing further is heard of him.

The council also sets 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 are rejected, and the practice of devotion to icons is confirmed.

Stephen is asked in 770 to confirm the election of Michael, a layperson, as Archbishop of Ravenna.

However, Michael, in league with the Lombard king Desiderius, and the Duke of Rimini have imprisoned Leo, who had been elected first.

Stephen refuses to confirm Michael’s election; citing the conventions of the Lateran council, he sends letters and envoys to Michael, demanding that he stand down.

Michael refuses, and the standoff will continue for over a year, until the arrival of the Frankish ambassador in Ravenna along with the Papal legates encourages Michael’s opponents to overthrow him, and send him to Rome in chains.

Leo follows soon after, when Stephen consecrates him as Archbishop of Ravenna.

Throughout his pontificate, Stephen is apprehensive about the expansionist plans of the Lombards.

Placing his hope in the Franks, he had attempted to mediate in the quarrels between Charlemagne and Carloman, which are only helping the Lombard’s cause in Italy.

He had helped them reconcile in 769, and pressured them to support the still infant Papal States, by reminding them of the support which their father had given the Papacy in the past.

He had also begged them to intercede on his behalf by entering into discussions with the Lombards.

Consequently, an embassy is sent to the Lombard king, Desiderius, in 770, which includes Charlemagne’s mother, Bertrada of Laon.

Their intervention achieves a result favorable to the Papacy by restoring to the pope the parts of Benevento that the popes claim.

To Stephen’s consternation however, Desiderius and Bertrada enter into discussions about a possible marriage between Desiderius’ daughter, Desiderata, and one Bertrada’s sons.

It is also possible that discussions took place around the marriage of Charlemagne’s sister, Gisela to Desiderius’ son, Adalgis.

Stephen therefore writes to both Charlemagne and Carloman, protesting about the proposed alliance.

Apart from noting that both men ware already married, he reminds 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.

His pleas fell on deaf ears, and Charlemagne marries Desiderata in 770, temporarily cementing a familial alliance with the Lombards.