It is highly likely that the former royal palace was initiated by the East Franconian Roman-German King Louis the German and existed until the beginning of the 11th century.[2] A moated castle is said to have existed on this site in the 13th century.[3] In 1462, the Mosbach court register mentions a castle house belonging to the Counts of Nassau with a moat and castle wall outside the village.[4] From 1654, the castle was owned by the Swedish ambassador Penz von Penzenau.
At the beginning of the 19th century, Duke Friedrich August von Nassau enlarged the Biebrich palace park and acquired the remains of the buildings that can be attributed to the imperial palace of Biburc (also Biburk). He commissioned Carl Florian Goetz to build a neo-Gothic residential castle on the ruins. The artificial ruin was completed between 1805 and 1806. Demolition material from the Church of Our Lady in Mainz was used for this. In the early 19th century, the castle was intended to embody the romantic idea of the Middle Ages.[5] The false ruin, which represents a contrast to the baroque Biebrich Castle, was used by the Dukes of Nassau as a place of retreat.[6]
After its completion, several epitaphs from the Eberbach monastery, which had been secularized in 1803, were brought to the castle for decoration. Among them were the gravestones of Johann II and Johann IV of Katzenelnbogen. They were returned to the monastery in 1936.[7] The gravestone of Diether V of Katzenelnbogen, which was also in the Mosburg at the same time, is now in the Wiesbaden Museum (Nassau Antiquities Collection).[8]
In the middle of the 19th century, the sculptor Emil Alexander Hopfgarten set up his studio in the Mosburg (see also: Wiesbaden painters and sculptors in the 19th century). After his death in 1856, his models and works were exhibited in the castle hall for another 18 years.[9]
From 1909 to 1945, the castle housed the Biebrich Local History Museum (in the so-called Knight's Hall).[10] The approval and a large part of the first furnishings were given by Wilhelm IV of Nassau-Weilburg.