Finished in 1259, Stolzenfels was used to protect the toll station at the Rhine, where the ships, back then were the main transport for goods, had to stop and pay toll. Over the years it was extended several times, occupied by French and Swedish troops in the Thirty Years' War and finally, in 1689, destroyed by the French during the Nine Years' War.
For 150 years the ruins decayed, until in 1815 they were given as a present to Frederick William IV of Prussia by the city of Koblenz. Following the romantic traditions, the prince started to completely rebuild the castle after 1826 as a summer residence. Supported by famous neoclassic architect Karl Friedrich Schinkel, the castle was completely remodeled in the then fashionable neo-Gothic style, aiming to create a romantic place representing the idea of medieval knighthood - the architects even created a tournament site.References:
The Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.