Veste Oberhaus castle dominates the old city of Passau, which it faces across the Danube. Below Oberhaus on the promontory between the two rivers is Veste Niederhaus, part of the fortress system.
The fortress was built in 1219 by Ulrich II, the first prince-bishop of Passau, at the location of a previously existing chapel dedicated to St. George. The intention was to express the military strength of the bishopric and support the bishop's status as an elector of the Holy Roman Empire, granted in 1217, and also to protect against both external enemies and internal threats such as those citizens of Passau who wished to acquire the independent status of a free imperial city.
As siege techniques improved over the centuries, Veste Oberhaus was repeatedly renovated and extended, beginning in 1255–56, so that it offers an opportunity to study fortification techniques from the 13th through the early 19th century. The most significant rebuilding took place under Leonhard von Laiming, Christoph von Schachner, Urban von Trennbach, and Johann Philipp von Lamberg. Under them, the fortress developed from a Gothic citadel to an early Renaissance princely residence, a 'fortified princely castle', and finally, in the era of invasion by the Turks, a regional fortress and symbol of aristocratic status. Archeological investigations in the 1990s revealed traces of a 17th-century residential tower.
The fortress was attacked five times between 1250 and 1482, each time without success. Twice, in 1298 and 1367, the attackers were the citizens of Passau themselves in rebellion against the bishop.
Between 1535 and 1540, numerous Protestant Anabaptists were imprisoned in the castle dungeon for their beliefs. During their imprisonment, the Ausbund hymnal, still used in Amish religious services, was developed. Some of the hymn writers died while imprisoned; many were martyred.
In 1704, 1742, and 1800 the fortress was forced to surrender to various forces. Secularization in 1802 brought an end to the rule of the bishop. Napoleon made use of the fortress during his campaign against Austria, placing it under the control of his allies the Bavarians as a border outpost, but in 1805 it surrendered to the Austrian army. After the Congress of Vienna the area was controlled by Bavaria and for almost a century, until 1918, the fortress served an additional purpose as a state and military prison.
In 1932 the City of Passau gained possession of Veste Oberhaus and instituted a museum, the Oberhausmuseum.
References:Ehrenbreitstein Fortress was built as the backbone of the regional fortification system, Festung Koblenz, by Prussia between 1817 and 1832 and guarded the middle Rhine region, an area that had been invaded by French troops repeatedly before. The fortress was never attacked.
Early fortifications at the site can be dated back to about 1000 BC. At about AD 1000 Ehrenbert erected a castle. The Archbishops of Trier expanded it with a supporting castle Burg Helferstein and guarded the Holy Tunic in it from 1657 to 1794. Successive Archbishops used the castle's strategic importance to barter between contending powers; thus in 1672 at the outset of war between France and Germany the Archbishop refused requests both from the envoys of Louis XIV and from Brandenburg's Ambassador, Christoph Caspar von Blumenthal, to permit the passage of troops across the Rhine.