In 724 the monastery was founded on the Reichenau Island in Lake Constance by the itinerant bishop Pirmin - apparently with the support of, among others, the Franconian major-domo Karl Martell. The Benedictine monk settled there with 40 fellow-believers, however moved on again after only three years. His successors developed a flourishing monastery from this basic group among the Carolingians, which produced important abbots with connections to the highest sovereigns of the age.
The monastery became an important stimulator for European civilization and grew to the religious and spiritual-cultural center of Europe. It was here, for example, that the famous monastery plan of St. Gall was drafted, a catalog of rules for monastery construction and one of the most important documents of Western monasticism. The monastery's abbots acted as government officials at the Court, as the educators of princes, diplomats and envoys of the Emperor.
The most important abbots of the monastery include Waldo, who traveled through Italy for Karl the Great, Heito I (806-822), Bishop of Basel and friend to Karl the Great and Wahlafried Strabo (838/842-849), a scholar and poet, who was also a teacher at the Court in Aachen. A herb garden, which grows on the same site as Wahlafried's own herb garden once grew in 840, still reminds us of him today.
In the 10th and 11th century the Abbey was the seat of a famous school of book illustration, the works of which can still be found today in the world's major libraries. The monks produced magnificent manuscripts with miniatures and splendid initials for influential customers such as Emperor Otto III ad Heinrich II. For this they used gold, silver, purple and for the bindings precious metals and ivory.
Of the Reichenau monastery library it was known throughout Europe in the early and high Middle Ages that it held hundreds of volumes. Today the State Library (Landesbibliothek) in Karlsruhe preserves what remains of these precious books, including 270 parchment manuscripts.
Pirmin's simple wooden church building already became a new abbey church in the early 9th century, of which parts of the nave and the side walls of the chancel have been preserved until today. In the centuries that followed, the existing cross basilica was often changed, rebuilt and enlarged. The early church from 816 always partially remained part of the house of God. Numerous monastery and administrative buildings and courtyards were built on the thriving monastery island and still mark the appearance of the island in the lake to this day.
During the "Golden Age" of Reichenau Island, numerous relics were collected. These precious objects are still kept in their splendid shrines in the treasure vault of the abbey church. On holidays they are carried across the island in festive processions. The most important relics include those of the evangelist Mark, the pitcher from the wedding at Kana and the Holy Blood relic.
Despite the high cultural and scientific level of the "reichen au" (rich meadowland), a decline came in the 11th century and the abbey was reduced to poverty. The causes of this decal include not only the increasing secularization of the abbots and "monastery lords", but also the devastating fire in 1235. Beginning in 1540 the Bishop of Constance, an old rival of the Reichenau abbots, was simultaneously the Lord of Reichenau. In 1803 the monastery fell to the State with the secularization movement and the abbey was disbanded.