The Diocese of Passau may be considered the successor of the ancient Diocese of Lorch (Laureacum).
At Lorch, a Roman station and an important stronghold at the junction of the Enns River and the Danube, Christianity found a foothold in the third century, during a period of Roman domination, and a Bishop of Lorch certainly existed in the fourth.
During the great migrations, Christianity on the Danube was completely rooted out, and the Celtic and Roman population was annihilated or enslaved.

In the region between the Lech River and the Enns, the wandering Baiuvarii were converted to Christianity in the seventh century, while the Avari, to the east, remained pagan.
The ecclesiastical organization of Bavaria was brought about by St. Boniface, who, with the support of Duke Odilo or at least enacting an earlier design of the duke, erected the four sees of Freising, Ratisbon, Passau, and Salzburg.
He confirmed as incumbent of Passau, Bishop Vivilo, or Vivolus, who had been ordained by Pope Gregory III, and who was for a long time the only bishop in Bavaria.
Thenceforth, Vivilo resided permanently at Passau, on the site of the old Roman colony of Batavis.
Here was a church, the founder of which is not known, dedicated to St. Stephen.
To Bishop Vivilo's diocese was annexed the ancient Lorch, which meanwhile had become a small and unimportant place.
By the duke's generosity, a cathedral was soon erected near the Church of St. Stephen, and here the bishop lived in common with his clergy.

The boundaries of the diocese extended westwards to the Isar river, and eastwards to the Enns.
In ecclesiastical affairs Passau was probably, from the beginning, suffragan to Salzburg.
Through the favour of Dukes Odilo and Tassilo, the bishopric received many gifts, and several monasteries arose—e.g.
Niederaltaich Abbey, Niedernburg Abbey, Mattsee Abbey, Kremsmünster Abbey—which were richly endowed.
Under Bishop Waltreich (774–804), after the conquest of the Avari, who had assisted the rebellious Duke Tassilo, the district between the Enns and the Raab River was added to the diocese, which thus included the whole eastern part (Ostmark) of Southern Bavaria and part of what is now Hungary.
The first missionaries to the pagan Hungarians went out from Passau, and in 866 the Church sent missionaries to Bulgaria.

Passau, the outermost eastern bulwark of the Germans, suffered most from the incursions of the Hungarians.
At that time many churches and monasteries were destroyed.
When, after the victory the Battle of Lech, the Germans pressed forward and regained the old Ostmark, Bishop Adalbert (946-971) hoped to extend his spiritual jurisdiction over Hungary.
His successor Piligrim (971-991), who worked successfully for the Christianization of Pannonia, aspired to free Passau from the metropolitan authority of Salzburg, but was completely frustrated in this, as well as in his attempt to assert the metropolitan claims which Passau was supposed to have inherited from Lorch, and to include all Hungary in his diocese.
By founding many monasteries in his diocese he prepared the way for the princely power of later bishops.
He also built many new churches and restored others from ruins.
His successor, Christian (991-1002) received in 999 from Emperor Otto III the market privilege and the rights of coinage, taxation, and higher and lower jurisdiction.
Emperor Henry II granted him a large part of the North Forest.
Henceforward, indeed, the bishops ruled as princes of the empire, although the title was used for the first time only in a document in 1193.
Under Berengar (1013–1045) the whole district east of the Viennese forest as far as Letha and March was placed under the jurisdiction of Passau.
During his time the cathedral chapter made its appearance, but there is little information concerning its beginning as a distinct corporation with the right of electing a bishop.
This right was much hampered by the exercise of imperial influence.

At the beginning of the Investiture Controversy, St. Altmann occupied the see (1065–1091) and was one of the few German bishops wh
The Diocese of Passau may be considered the successor of the ancient Diocese of Lorch (Laureacum). At Lorch, a Roman station and an important stronghold at the junction of the Enns River and the Danube, Christianity found a foothold in the third century, during a period of Roman domination, and a Bishop of Lorch certainly existed in the fourth. During the great migrations, Christianity on the Danube was completely rooted out, and the Celtic and Roman population was annihilated or enslaved.
In the region between the Lech River and the Enns, the wandering Baiuvarii were converted to Christianity in the seventh century, while the Avari, to the east, remained pagan. The ecclesiastical organization of Bavaria was brought about by St. Boniface, who, with the support of Duke Odilo or at least enacting an earlier design of the duke, erected the four sees of Freising, Ratisbon, Passau, and Salzburg. He confirmed as incumbent of Passau, Bishop Vivilo, or Vivolus, who had been ordained by Pope Gregory III, and who was for a long time the only bishop in Bavaria. Thenceforth, Vivilo resided permanently at Passau, on the site of the old Roman colony of Batavis. Here was a church, the founder of which is not known, dedicated to St. Stephen. To Bishop Vivilo's diocese was annexed the ancient Lorch, which meanwhile had become a small and unimportant place. By the duke's generosity, a cathedral was soon erected near the Church of St. Stephen, and here the bishop lived in common with his clergy.
The boundaries of the diocese extended westwards to the Isar river, and eastwards to the Enns. In ecclesiastical affairs Passau was probably, from the beginning, suffragan to Salzburg. Through the favour of Dukes Odilo and Tassilo, the bishopric received many gifts, and several monasteries arose—e.g. Niederaltaich Abbey, Niedernburg Abbey, Mattsee Abbey, Kremsmünster Abbey—which were richly endowed. Under Bishop Waltreich (774–804), after the conquest of the Avari, who had assisted the rebellious Duke Tassilo, the district between the Enns and the Raab River was added to the diocese, which thus included the whole eastern part (Ostmark) of Southern Bavaria and part of what is now Hungary. The first missionaries to the pagan Hungarians went out from Passau, and in 866 the Church sent missionaries to Bulgaria.
Passau, the outermost eastern bulwark of the Germans, suffered most from the incursions of the Hungarians. At that time many churches and monasteries were destroyed. When, after the victory the Battle of Lech, the Germans pressed forward and regained the old Ostmark, Bishop Adalbert (946-971) hoped to extend his spiritual jurisdiction over Hungary. His successor Piligrim (971-991), who worked successfully for the Christianization of Pannonia, aspired to free Passau from the metropolitan authority of Salzburg, but was completely frustrated in this, as well as in his attempt to assert the metropolitan claims which Passau was supposed to have inherited from Lorch, and to include all Hungary in his diocese. By founding many monasteries in his diocese he prepared the way for the princely power of later bishops. He also built many new churches and restored others from ruins. His successor, Christian (991-1002) received in 999 from Emperor Otto III the market privilege and the rights of coinage, taxation, and higher and lower jurisdiction. Emperor Henry II granted him a large part of the North Forest. Henceforward, indeed, the bishops ruled as princes of the empire, although the title was used for the first time only in a document in 1193. Under Berengar (1013–1045) the whole district east of the Viennese forest as far as Letha and March was placed under the jurisdiction of Passau. During his time the cathedral chapter made its appearance, but there is little information concerning its beginning as a distinct corporation with the right of electing a bishop. This right was much hampered by the exercise of imperial influence.
At the beginning of the Investiture Controversy, St. Altmann occupied the see (1065–1091) and was one of the few German bishops wh
Roman Catholic Diocese of Passau