Petershausen Abbey was founded as an exempt abbey named after Saint Peter in 983 by Bishop Gebhard of Constance, located on the northern shore of the Rhine river opposite to the episcopal residence at Constance with its cathedral. Gebhard dedicated the monastery church to Pope Gregory the Great and settled the abbey with monks descending from Einsiedeln.
Under Bishop Gebhard III of Zähringen and Abbot Theodoric (1086–1116), the Hirsau Reforms were introduced. In 1097 a filial monastery was established at Mehrerau near Bregenz. As Petershausen sided with the papacy in the Investiture Controversy, Gebhard III in 1103 was deposed at the instigation of Emperor Henry IV. The abbey was closed until 1106, the monks fled to the newly established Kastl Abbey in Bavaria. In 1159 the monastery burnt down, and was rebuilt and extended between 1162 and 1180. Facing the claims of Swabian nobles like the Counts of Montfort, the abbots became supporters of the Imperial Hohenstaufen dynasty. Under Emperor Frederick II (1220–50), Petershausen became reichsfrei, gaining territorial independence.
During the Council of Constance (1414–18), the German king Sigismund of Luxembourg stayed at the abbey and the Petershausen abbot even gained the pontifical vestments from Antipope John XXIII. Nevertheless the monastery declined during the 14th and 15th centuries, pressed hard by Konstanz claiming the status of an Imperial city, as well as by the diocese. The attempts of Prince-Bishop Hugo von Hohenlandenberg to incorporate Petershausen were blocked by Emperor Maximilian I of Habsburg. The abbey was charged by the Konstanz citizens during the Protestant Reformation and the brothers were expelled. It was again ravaged by Imperial troops during the Schmalkaldic War, after which the City of Konstanz in 1548 was incorporated into the Habsburg possessions of Further Austria. The monks did not return until 1556.
Petershausen was finally secularised to Baden in 1802; the library was bought by the University Library Heidelberg. Margrave Charles Frederick of Baden had parts of the abbey rebuilt as a private residence for his sons. The St Gregory Church was demolished in 1832. The remaining premises were later used as a psychiatric hospital and as barracks. They now accommodate a number of administrative and educational functions and the Archaeological Museum of Baden-Württemberg.References:
From its origin as a small stronghold built by the ancient Illyrian tribe Dalmatae, becoming a royal castle that was the seat of many Croatian kings, to its final development as a large fortress during the Ottoman wars in Europe, Klis Fortress has guarded the frontier, being lost and re-conquered several times. Due to its location on a pass that separates the mountains Mosor and Kozjak, the fortress served as a major source of defense in Dalmatia, especially against the Ottoman advance, and has been a key crossroad between the Mediterranean belt and the Balkan rear.
Since Duke Mislav of the Duchy of Croatia made Klis Fortress the seat of his throne in the middle of the 9th century, the fortress served as the seat of many Croatia"s rulers. The reign of his successor, Duke Trpimir I, the founder of the Croatian royal House of Trpimirović, is significant for spreading Christianity in the Duchy of Croatia. He largely expanded the Klis Fortress, and in Rižinice, in the valley under the fortress, he built a church and the first Benedictine monastery in Croatia. During the reign of the first Croatian king, Tomislav, Klis and Biograd na Moru were his chief residences.
In March 1242 at Klis Fortress, Tatars who were a constituent segment of the Mongol army under the leadership of Kadan suffered a major defeat while in pursuit of the Hungarian army led by King Béla IV. After their defeat by Croatian forces, the Mongols retreated, and Béla IV rewarded many Croatian towns and nobles with 'substantial riches'. During the Late Middle Ages, the fortress was governed by Croatian nobility, amongst whom Paul I Šubić of Bribir was the most significant. During his reign, the House of Šubić controlled most of modern-day Croatia and Bosnia. Excluding the brief possession by the forces of Bosnian King, Tvrtko I, the fortress remained in Hungaro-Croatian hands for the next several hundred years, until the 16th century.
Klis Fortress is probably best known for its defense against the Ottoman invasion of Europe in the early 16th century. Croatian captain Petar Kružić led the defense of the fortress against a Turkish invasion and siege that lasted for more than two and a half decades. During this defense, as Kružić and his soldiers fought without allies against the Turks, the military faction of Uskoks was formed, which later became famous as an elite Croatian militant sect. Ultimately, the defenders were defeated and the fortress was occupied by the Ottomans in 1537. After more than a century under Ottoman rule, in 1669, Klis Fortress was besieged and seized by the Republic of Venice, thus moving the border between Christian and Muslim Europe further east and helping to contribute to the decline of the Ottoman Empire. The Venetians restored and enlarged the fortress, but it was taken by the Austrians after Napoleon extinguished the republic itself in 1797. Today, Klis Fortress contains a museum where visitors to this historic military structure can see an array of arms, armor, and traditional uniforms.