The Michaelskloster on the Heiligenberg only exists as a ruin today.
The builder of the first church around the year 870 was probably Abbot Thiotroch von Lorsch. Only in 1023 was Saint Michael built in the same location as can be seen from the remains of the foundation.
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 (grave slab in the crypt of the basilica). Thus the monastery became a place of pilgrimage (not canonized).
In the 11th century, the Michaelskloster started a daughter monastery at the front summit of the Heiligenberg. It was the Stephansloster. The three last monks in Michael's monastery were slain 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 monasteries and sell the stones. But nothing happened, as Merian's engraving from 1645 shows. It was not until 1860 that someone first drew attention to the remains of mighty stone walls that surrounded the tops of the mountain. At first they were ascribed to Roman or medieval times. Excavations revealed that they went much further back.