The Benedictine abbey of Saint Mang was founded in the first half of the 9th century as a proprietary monastery of the Prince-Bishops of Augsburg. The reason for its foundation goes back to the hermit Magnus of Füssen (otherwise known as Saint Mang), who built a cell and an oratory here, where he died on 6 September, although there is no record of which year.
The saint's body, amid miracles, was discovered uncorrupted, a proof of his sanctity, and the veneration of St. Mang was the spiritual basis of the monastery.
The foundation was not however solely spiritually motivated; there were practical political reasons underlying it as well. The monastery's key position not only on the important medieval road from Augsburg across the Alps to Upper Italy but also in the Füssen Gap ("Füssener Enge", the point where the Lech River breaks out of the Alps) gave it an immense strategic value, which made it of political concern both to the Bishops of Augsburg and to the Holy Roman Emperors.