Monasterio de San Juan was founded in 1091, when the kings Alfonso VI and Constance of Burgundy donated a small land to monk Lesmes, who came from the Chaise-Dieu abbey. In 1537 a fire destroyed practically the whole monastery. The reconstruction lasted until the confiscation. During the first half of the 19th century, several confiscations destroyed the heritage of the monastery and the hospital of San Juan. The monks were expelled from the monastery. The buildings were used as a prison.
Ehrenbreitstein Fortress was built as the backbone of the regional fortification system, Festung Koblenz, by Prussia between 1817 and 1832 and guarded the middle Rhine region, an area that had been invaded by French troops repeatedly before. The fortress was never attacked.
Early fortifications at the site can be dated back to about 1000 BC. At about AD 1000 Ehrenbert erected a castle. The Archbishops of Trier expanded it with a supporting castle Burg Helferstein and guarded the Holy Tunic in it from 1657 to 1794. Successive Archbishops used the castle's strategic importance to barter between contending powers; thus in 1672 at the outset of war between France and Germany the Archbishop refused requests both from the envoys of Louis XIV and from Brandenburg's Ambassador, Christoph Caspar von Blumenthal, to permit the passage of troops across the Rhine.