Maximian, the bishop of Ravenna, endows the monastery of St. Andrew and the church of St. Mary in Pula.
Pope Pelagius I writes to patrician John regarding the detrimental consequences of the schism within the Church (the so-called Three Chapters Controversy), especially concerning the recent election of a schismatic patriarch of Aquileia, urging the Byzantine official not to recognize their authority as they had not been canonically elected.
Pope Pelagius I writes to patrician Valerian, urging him to take action against the schismatic bishops in the ecclesiastical provinces of Milan and Aquileia and support the papal quest to bring back unity to the Church.
Lombards under King Alboin invade Italy and conquer Friuli; Gisulf I, Alboin's nephew, is made the ruler (duke) of Friuli; Paulinus, the incumbent patriarch of Aquileia, flees from Aquileia due to the invasion and finds shelter in Grado where he hides the treasury of his Church as well (narrative account from Paul the Deacon's History of the Lombards).
Pope Pelagius II confirms Grado as the new metropolitan see of the ecclesiastical province of Venetia et Histria; 11th-century forgery.
The acts of the synod of Grado, heavily interpolated by later falsifications, by which the bishops of the ecclesiastical province of Aquileia remain faithful to the Catholic creed as decreed by the Ecumenical Councils of Chalcedon (451), Ephesus (431), Constantinople I (381) and Nicaea (325), refusing to denounce the Three Chapters condemned by the Second Ecumenical Council of Constantinople (552).
Pope Pelagius II writes to Helias, the patriarch of Aquileia, and all the bishops of Istria, the province whose prelates still persevered in their refusal to condemn the three chapters denounced by the Fifth Ecumenical Council (Constantinople II) of 553, urging them to desist from their schismatic ways and return to the embrace of the Catholic Church.
Following the death of Aquileian patriarch Helias, his successor, Patriarch Severus, together with three other bishops (including the bishop of Poreč, John) are imprisoned in Ravenna by the Byzantine exarch Smaragdus; in order to buy their freedom, the prelates agree to condemn the Three Chapters and reunite with Rome, a move that greatly angers other bishops in the ecclesiastical province of Aquileia. Finally, a synod is held in Marano (591) whereby Patriarch Severus is forced to formally acknowledge the error of his ways in supporting the condemnation of the Three Chapters (narrative accounts from Paul the Deacon's History of the Lombards).
Pope Gregory I writes to Severus, the patriarch of Aquileia, requesting on behalf of the emperor (Maurice) that he come to Rome with his clergy and be judged on a synod (for his unwillingness to condemn the Three Chapters and his perseverance in supporting the schism).
The bishops of the ecclesiastical province of Aquileia write to emperor Maurice, beseeching him not to allow their metropolitan, Archbishop Severus of Aquileia, who was forcefully taken to the pope in Rome, to be put on trial and judged by the adversaries of the Three Chapters, that is, the non-schismatic clergy; the bishops expound their viewpoints on the theological controversy, their fealty to the Ecumenical Council of Chalcedon, and why they refuse to denounce the so-called Three Chapters condemned by Emperor Justinian I and the Ecumenical Council of Constantinople in 553.
Emperor Maurice writes to Pope Gregory I, urging him not to treat violently the schismatic bishops of the ecclesiastical province of Aquileia (the "Istrian bishops") and not to compel them to journey to Rome.
Following the death of Aquileian patriarch Severus, two new patriarchs are ordained: John, supported by the Lombards and with his seat in Aquileia; and Candidianus, supported by the Romans (Byzantines) with his seat in Grado - the definitive and official split of the patriarchate of Aquileia into two patriarchal sees (narrative account from Paul the Deacon's History of the Lombards).
Patriarch John of Aquileia writes to Lombard King Agilulf, complaining that the ill-ordained Candidianus was consecrated as the bishop of Grado by the three Istrian bishops who were violently forced to do so by the “Greeks” (the Romans, that is, the Byzantines), and he beseeches the king not to allow such consecrations to continue following Candidianus' death.
Under Lombard King Cunipert, the Synod of Pavia takes place where the representatives of the schismatic clergy of the ecclesiastical province of Aquileia officially accept the decrees of the 5th Ecumenical Council (Constantinople II) and finally desist from their schism; narrative account from the contemporary "Poem on the Synod of Pavia" (Carmen or Rythmus de Synodo Ticiensi).
Late 8th-century poem lamenting the destruction of Aquileia at the hands of the Huns in the mid-5th century, composed either by Paulinus II of Aquileia (ⴕ 802) or Paul the Deacon; the poem was later used by Venetian authors to argue that Aquileia had never been restored following this destruction and that Grado, therefore, succeeded it as the capital of the ecclesiastical province of Venetia et Histria.
King Charlemagne bestows to the Church of Aquileia the right to canonical election of their patriarchs (that nonetheless requires royal confirmation) and exempts it from public taxes such as the tithes, the grazing fees for livestock sent to graze in Istria, and war taxes (lodgings and provisions for the army) unless the royal military is forced to pass through Friuli and the Treviso region.
King Charlemagne confirms the possessions of the Church of Aquileia and grants it immunities.
A poem dedicated to the memory of the late Duke Eric of Friuli, composed by Patriarch of Aquileia Paulinus II.
Emperor Charlemagne subordinates six episcopal sees to the Church of Aquileia, badly damaged by the incursions of the pagans; late-10th-century forgery.
The decrees of the Synod of Mantua: the long conflict between the patriarchs of Grado and Aquileia over the metropolitan jurisdiction over Istrian bishoprics is settled in favor of the Aquileian Church.
Emperor Lothair I confirms the immunities enjoyed by the Church of Aquileia and its right to canonically elect their patriarchs.
A poem composed in response to the Synod of Mantua (6th of June, 827), arguing that Aquileia, the old metropolitan see of the ecclesiastical province Venetia et Histria, was so thoroughly destroyed by barbarians (Attila, the Avars, Lombards and Goths) that it was never rebuilt; thus, the metropolitan see transferred to "the Venetians" and Aquileia was demoted to a status of a mere parish.
Emperor Louis II confirms the charter of Lothair I to the Patriarchate of Aquileia regarding the dispute with the Patriarchate of Grado that was settled at the Synod of Mantua in 827: the patriarchs of Aquileia are to enjoy the metropolitan jurisdiction over all the Istrian bishoprics.
Hugh of Arles and his son Lothair II, kings of Italy, donate Muggia to the Patriarchate of Aquileia.