Pope Adrian I writes to Charlemagne, the King of the Franks and the Lombards, beseeching him to direct Duke Marcarius of Friuli to help reinstate the Istrian bishop Maurice – whose eyes have been gouged out by “the most abominable Greeks” – to his bishopric.
Narrative sources on the events of 788 that resulted, among a variety of other things, with Istria being incorporated into the Frankish kingdom.
King Charlemagne writes to his wife Fastrada, informing her, among other things, of their military successes against the Avars, including the achievements of his “duke of Istria”. This is the first documented mention of a Carolingian official in Istria, officially marking the beginning of a new era of the peninsula’s history.
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.
Pope Leo III confers the pallium upon Fortunatus II, the incumbent patriarch of Grado.
Emperor Charlemagne subordinates six episcopal sees to the Church of Aquileia, badly damaged by the incursions of the pagans; late-10th-century forgery.
Emperor Charlemagne bestows immunities upon the Church of Grado due to the special services and merits of its incumbent Patriarch Fortunatus II.
Emperor Charlemagne exempts the four ships of Fortunatus II, "the patriarch of the Venetians and Istrians," from all the tolls.
Pope Leo III writes to Emperor Charlemagne regarding the situation of Fortunatus, the patriarch of Grado who had been exiled from his see by the Venetians and "the Greeks". The pope agrees that the Church of Pula should be bestowed upon Patriarch Fortunatus as his new seat.
Emperor Louis the Pious informs Patriarch Fortunatus II of Grado and the faithful of the province of Istria that, at their request, he confirms the free election of the patriarch, bishops, abbots, tribunes and other authorities, that in the event of breach of faith, quarrels and oppression of the poor, the legal judgment awaits them and that violators of the Placitum of Rižana (doc. 804_PR) will be subject to the prescribed penance.
Emperor Louis the Pious and his son Lothar write to Venerius, the patriarch of Grado, confirming the possessions of his Church, including the Patriarchate's jurisdictions in Istria.
Louis the Pious and his son Lothar instruct Patriarch Venerius of Grado to go to Rome again to settle his dispute with the Patriarch Maxentius of Aquileia before the Pope and their messengers, despite the fact that Maxentius failed to attend the first meeting, causing Venerius to return home without any resolution.
Emperor Louis the Pious deposes several marcher officials – including Baldric, the duke of Friuli – from their offices due to their military impotence. As a result of Baldric’s deposition, the March of Friuli – which included Istria – is divided into four counties governed by their respective counts.
Emperor Lothair I confirms the immunities enjoyed by the Church of Aquileia and its right to canonically elect their patriarchs.
The first pact between the Venetian neighbors in the Kingdom of Italy, represented by Emperor Lothar I, and the Duchy of Venice, represented by Doge Pietro Tradonico, sanctioning mutual aid in campaigns against the Slavs, defining the rights over the use of land and numerous aspects related to trade as well as the modalities of justice administration.
Emperor Lothar I confirms the Venetian possessions in the Empire.
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.
Pope Sergius II writes to Andrew, the patriarch of Aquileia, addressing his ongoing dispute with Venerius, the patriarch of Grado, urging patience, suggesting the convening of a general synod to address these issues, and emphasizing the need for imperial authority to finally put an end to this dispute between the two ecclesiastical sees.
Pope Leo IV writes to Victor, the patriarch of Grado, conferring upon him the pallium.
Emperor Louis II assumes under his protection the monastery of St. Michael in Diliano and its abbot Felmo, bestowing upon the monastery immunities and the right of free election of its abbots.
Emperor Louis II confirms the charter of Lothar I to the Patriarchate of Aquileia regarding the dispute with the Patriarchate of Grado that was settled at the Synod of Mantua in 827 (doc. 827_SM): the patriarchs of Aquileia are to enjoy the metropolitan jurisdiction over all the Istrian bishoprics.
Emperor Louis II confirms to St. Michael's monastery in Diliano and abbot Felmo the right to have two lay advocates - the brothers Petronasius and Talasius - to defend their rights.
Pope Benedict III writes to Vitalis, the patriarch of Grado, conferring upon him the pallium.
After having invaded and conquered Italy, King Otto I convokes a diet in Augsburg whereby he bestowed upon the defeated Berengar II and his son Adalbert the Kingdom of Italy, albeit somewhat reduced: the marches of Verona and Aquileia were ripped off from Italy and appended to the Duchy of Bavaria, governed by Otto's brother Henry. Since Istria formed part of the "March of Aquileia" (i. e. Friuli), this event marks the beginning of a new chapter of Istrian history.