The use of the site for religious buildings is believed to date from around 790, when a Benedictine monastery was established here, to which were brought the relics of Saint Hippolytus, after whom the present city is named.

In 828, the monastery became a possession of the Diocese of Passau, and a centre of missionary activity, predominantly in Great Moravia.

The first documentary reference is in a charter of 976 from Emperor Otto II to Bishop Pilgrim of Passau.

Under Bishop Altmann of Passau the abbey became an Augustinian canonry, which was dissolved in 1784 as part of the Josephine Reforms.

In 1228 Bishop Gebhard changed the dedication, formerly to Saints Peter, Stephen and Hippolytus, to the Assumption of Mary.