A small monastery was founded in Altomünster by Saint Alto, a wandering monk, in about 750. The vita of Alto, likely written by Otloh of St. Emmeram after 1056 and ostensibly based on oral knowledge (written lore having been lost through plunder), reports that the monastery was visited by Saint Boniface, who dedicated the church. Another 11th-century text notes that Boniface also dedicated the church in nearby Benediktbeuern Abbey.
Sometime before 1000 the Welfs enlarged it and made it into a Benedictine abbey. Welf I, Duke of Bavaria resettled the monks in 1056 to the newly founded Weingarten Abbey in Altdorf, while the nuns formerly resident at Altdorf moved to Altomünster, where they lived until the monastery was dissolved in 1488 by Pope Innocent VIII.
In 1496 by grant of Duke George the Rich the Bridgettines of Maihingen were permitted to establish a Bridgettine monastery at Altomünster. The monastery was dissolved on 18 March 1803 during the secularisation of Bavaria, but was later revived. Today, along with a settlement in Bremen, it is the last Bridgettine monastery in Germany. Nearby is a museum of the history of the Bridgettine Order.
Two gospel lectionary created for the abbey in the 12th century are held by the Bavarian State Library.
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.