It is the place from which the Heiligenberg got its name, because in the Middle Ages the mountain was still called "All Saints' Mountain", "mons omnium sanctorum" and was consecrated to all saints. The name Heiligenberg is linked to the consecration formula under which the old St. Michael's Monastery was founded on the hilltop behind the mountain: "...in honour of St. Michael the Archangel and all the saints".
The first church was probably built around 870 by Abbot Thiotroch of Lorsch. It was not until 1023 that St Michael's was built in the same location, as can be seen from the remains of the foundations.
Abbot Reginbald, who later became Bishop of Speyer, had the monastery rebuilt using Carolingian components. In 1070, Abbot Friedrich von Hirsau was buried in the monastery (tombstone in the crypt of the basilica). The monastery thus became a place of pilgrimage (not canonised).
In the 11th century, a daughter monastery was founded by St Michael's Monastery on the front hilltop of the Heiligenberg. This was St Stephen's Monastery. The last three monks in St Michael's Monastery were killed in their beds by the collapsing crossing tower of the church in 1503. The monastery was dissolved and fell into oblivion.
In 1589, the Senate of Heidelberg University decided to demolish the monastery and sell the stones. But nothing happened, as Merian's engraving from 1645 shows. It was not until around 1860 that someone first drew attention to the remains of mighty stone ramparts that stretched around the hilltops. They were initially attributed to Roman or medieval times. Excavations revealed that they dated back much further.
