The Plea of Rižana (Placitum Rizianense): The representatives of Istrian towns and cities present their grievances to counts Aio and Cadulus, the envoys of the Roman emperor Charlesmagne, in an official placitum held by the river Rižana in the district of Koper.
Emperor Louis the Pious promises to Patriarch Fortunatus II and to all the Istrians that their right to elect their own patriarchs, bishops, abbots, tribunes, and other officials will be respected and that the rulings of the judicial assembly (placitum) held by Rižana will be upheld.
Emperor Louis the Pious and his son Lothair write to Venerio, the patriarch of Grado, confirming the possessions of his Church, including the Patriarchate's jurisdictions in Istria.
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 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 Western Roman Empire, represented by Emperor Lothair I, and the Duchy of Venice, represented by Doge Pietro Tradonico, sanctioning mutual aid in campaigns against the Slavs and defining the rights over the use of land as well as the modalities of justice administration. This is the first "international" treaty in which Venice partook as an autonomous polity, independent of the Byzantine 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.
The last will and testament of a woman from Trieste calling herself "Maru, the handmaiden of God" (Maru ancilla Dei).
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 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.
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.
Venice, represented by Doge Orso I Participazio, and the Patriarchate of Aquileia, represented by Patriarch Walpert, sign a treaty according to which the Venetian Doge agrees not to block the Aquileian port Pylum, but only under the condition that the patriarch stops with all the hostilities directed against the Church of Grado and exempts the Venetians from all the tolls on his territories, according to the old customs.
Pope Sergius III writes to John, the bishop of Pula, informing him of Archbishop of Ravenna John XI's complaints against Count Albuin, who unlawfully alienated the possessions of the Church of Ravenna in Istria, and asking him to personally convey to the Count that he must return these possessions under the threat of excommunication and that King Berengar I will not be crowned emperor until he grants Albuin’s March (of Istria or of Friuli) to someone better.
King Berengar I donates two forts, the Vermes (Beram in Istria ?), to the Bishopric of Trieste (10th- or 11th-century forgery).
King Hugo donates Sipar, Umag, and Monfalcone to Radald, the bishop of Trieste, and places the Bishopric of Trieste under his royal protection; a forged charter.
Hugh of Arles and his son Lothair II, kings of Italy, donate Muggia to the Patriarchate of Aquileia.
Due to fair treatment and protection, the city of Koper, represented by a locopositus, scabini, the protector of the people (advocatus totius populi) and many others, freely promise an annual tribute of one hundred amphorae of wine to Venice, to be paid every year within ten days of the harvest, and protection to all Venetians.
Thanks to the mediation of Marino, the patriarch of Grado, Lupus II, the patriarch of Aquileia, manages to reach a peace accord with Venice, represented by Doge Pietro III Candiano, but only under the condition that all the hostilities directed against Grado immediately stop and that the patriarch promises to inform Venice of any hostile plans directed against it.
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.
The eastern borders of the province of Istria (and the Kingdom of Italy / Holy Roman Empire) according to the 10th-century work customarily titled De administrando imperio and ascribed to Eastern Roman Emperor Constantine VII Porphyrogenitus.
Patriarch Rodoald donates Rovinj, a land that was destroyed by the "abominable Slavs", to the Bishopric of Poreč. Forged charter.
Excerpts from the family chronicle of the counts of Sempt-Ebersberg regarding Ulrich I, the count of the march of Carniola; his heirs Adalbero II, Eberhard II and Williburga II; and Hademoud II, the daughter of Williburga II and the only surviving direct heir of House Sempt-Ebersberg. Hademoud II would marry Poppo II of Weimar-Orlamünde with whom she would have Ulrich I, the first margrave of Istria.