The predecessor of today's Mosburg in Biebrich Palace Park, a moated castle, was probably built by the Nassau family in the 14th or 15th century, sold in 1654, fell into disrepair in 1776 and was once again owned by Nassau from 1804. In 1806-16, Carl Florian Goetz built a medieval-looking romantic residential castle on its foundations, situated on a peninsula in the later created Mosburg pond (1818-23) and with its own castle garden. Duke Friedrich August zu Nassau had it magnificently furnished with original works of art.

Primarily a private retreat, it also provided a glamorous setting for social receptions and princely celebrations. Under Duke Adolph, the Mosburg served as a studio for the sculptor Emil Alexander Hopfgarten from around 1849-56. His works here included the sarcophagus of Duchess Elisabeth zu Nassau for the Russian Orthodox Church of St. Elisabeth and sculptures for St. Boniface and the Marktkirche. After Hopfgarten's death, his works and models could still be viewed in the Mosburg until 1874. In 1862, during walks with Duke Adolph, Richard Wagner discovered the idyllic Mosburg as a possible place to live and work. His wish to move in was not fulfilled. From 1909, the Mosburg housed the newly founded Biebrich Museum of Local History, which was plundered during the Second World War and eventually closed down.

The castle itself fell into disrepair within a very short space of time, as penetrating moisture destroyed the wooden structures of the flat sloping roofs. The ruins of Mosburg Castle are owned by the state of Hesse.