The monastery was established as the first in the medieval Duchy of Carinthia in about 1024 by a certain Count Ozi, affiliated with the Styrian Otakar dynasty and father of Patriarch Poppo of Aquileia. The first monks were probably from Niederaltaich Abbey in Bavaria. From the Otakars the Vogtei of Ossiach passed to the Austrian House of Babenberg and finally fell to the Habsburgs.
According to legend, King Bolesław II the Bold of Poland, after he was banished in 1079 for the murder of Saint Stanislaus of Szczepanów and had fled to Hungary, then wandered through Europe and found peace at last when he arrived at Ossiach. There the king is said to have lived in the monastery as a mute penitent for eight years humbly doing the meanest and lowliest jobs, until on his death bed he told his father confessor who he was and what he had been doing penance for. The Latin inscription on his alleged tomb at the northern side of the church building says, "Boleslav, King of Poland, Murderer of Saint Stanislav, Bishop of Cracow".
The Romanesque church itself was first mentioned in 1215, built on the groundplan of a basilica, with the tower above the crossing. Restored in a Late Gothic style after a fire in 1484, the abbey, a member of the Benedictine Salzburg Congregation from 1641, was extensively altered in the Baroque period, including stucco decoration of the Wessobrunner School.
Ossiach Abbey was dissolved in 1783, after which the buildings were used as a barracks. In 1816 the premises were largely demolished. Between 1872 and 1915 the few remaining buildings were again used as a barracks and as stabling. Since 1995 the premises have been owned by the administration of Carinthia. The church since the dissolution has served the local parish. Two stained glass windows were donated by Karl May in 1905, though according to recent research the popular writer had probably never visited Ossiach.
The monastery site is one of the venues of the annual music festival "Carinthian Summer".
- Alois Pischinger, Sagen aus Österreich. Vienna: Carl Ueberreuter 1949, pp. 233-235
- Gustav Renker, Wilhelm Brauneder, Willi Rainer, Karl May in Ossiach. In: Wilhelm Brauneder (ed.), Karl May und Österreich. Husum: Hansa 1996, pp. 88–97 .ISBN: 3920421698 and
Wilhelm Brauneder, Die May-Fenster zu Ossiach: Was tatsächlich geschah. In: M-KMG 150/2006, pp. 72-76
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