The chapel dedicated to the patron saint St. Erasmus is already mentioned in a document from around 889 AD.
King Arnulf confirms the donation of "chapel and farms in Piscofesdorf" (later Piesdorf) to the monastery and Archabbot Thietmar of St. Peter in Salzburg. This document also shows that "that area had already been consecrated to God". It is therefore assumed that the Attergau was the missionary territory of Bishop Rupert of Salzburg.
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