Even before the Lombard conquest, which altered the continuity of the territory and split it into the Adriatic part and the inland, in the ecclesiastic communion there had been a profound tearing between the Church of the Empire and the Churches of the metropolitan province of Aquileia. The majority of Latin bishops, among whom also the bishops of the province of Aquileia, broke their communion with Rome and the Church of the Empire following the edict by Justinian who in 542-543 had condemned the texts of three authors (Theodore of Mopsuestia, Theodoret of Cyrus and Ibas of Edessa), briefly known as the Three Chapters, whose theological contributions had been acknowledged orthodox by the preceding council of Chalcedonia (451). In the 2nd Council of Constantinople (553-554), in his attempt to put an end to a dispute that had occurred between opponent theological schools, Justinian had the three theologians condemned, though they were already dead. Under the emperor’s pressure also pope Vigilius, after wavering, had eventually to give his consent to this condemnation, and that brought to the reaction of some of the most important Western Churches, among which Aquileia, that got away from Rome. The election of Paul [Paolo] to the cathedra of Aquileia occurred in a climate of heated anti-Constantinopolitan opposition and doctrinal independence from Rome. In 557 Paul [Paolo] called a synod of the provincial bishops and with them he proclaimed his radical loyalty to the Council of Chalcedonia and the refusal of the decisions that had been taken at Constantinople and ratified by pope Vigilius. The violent pressures that were exerted on the Aquileian Church to put the schism to an end led also to the double patriarchal election in the year 606, that had as a consequence the contraposition of a patriarch of Aquileia in the Lombard inland and a patriarch of Grado elected with the support of the Byzantine army. For over a century, until the year 698, the autocephaly of the ecclesiastical province of Venetia et Histria was prolonged by the Aquileian metropolitans, who strengthened their title of Venetiarum atque Histriae patriarcha, patriarch of Venice and Istria.
Following the Justinian’s edict, the schism brought to profound tearing: the bishopric of Aquileia broke its communion with Rome and the Church of the Empire