Isen Abbey was a Benedictine abbey, later a collegiate foundation. Dedicated to Saint Zeno of Verona, the abbey was founded by members of the Fagana family, an indigenous Bavarian noble clan, and by Bishop Joseph of Freising (also known as Joseph of Verona) in the 8th century, about 752. It was one of the oldest monasteries on ancient Bavarian soil. Until the beginning of the 12th century it was Benedictine, but afterwards became a collegiate foundation.
It was dissolved during the secularisation of Bavaria in 1802. The premises and the abbey's seven farms passed into private ownership, while St. Zeno's church, with a house for the priest, became the parish church of Isen.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.