Cyriaksburg Castle is located on a hill at the gates of the Thuringian state capital of Erfurt. It was an important part of the city's fortifications. Cyriaksberg was a strategically important point from which enemy troops could fire on the city. After 1815, the Prussian government of the time elevated Erfurt to a first-class fortress city with two citadels. The Cyriaksburg fort from 1480 was converted into a fortress in the neo-Prussian style (today's situation) by the engineer captain Haak.

Today, two mighty round towers from 1528 and 1530 as well as the remains of the walls still bear witness to the former state of construction. Swedish troops reinforced the fort during the Thirty Years' War. In the 17th and 18th centuries, the military importance of Cyriaksburg Castle declined, so much so that the Erfurt city council even considered demolishing it. During the Napoleonic period from 1806 to 1813, the castle was under French occupation.

Before the construction of Cyriaksburg Castle began, there was a Benedictine nunnery, the Cyriakskloster, on roughly the same site until 1478. Remains of the former convent can no longer be seen today.

Most of the parts of the building that are still visible today date from the period between 1825 and 1829. Cyriaksburg Fortress was given a so-called defensive barracks as its main building, which housed teams and officers who were specifically responsible for operating the cannons. Riflemen could fire their guns through embrasures into the moat and the entrance to the fortress. The roof was protected from bullets by a thick layer of earth. The underground war well can still be visited inside the fortress today. The entrance and the brick domed vault were built in 1829. Before this time, the well, which was dug in 1530, stood outside. A cistern has stored around 8 m³ of water since 1829. Today, the well is approx. 40 m deep. From 1871, the water was pumped by a pump installed at the bottom of the well. Cyriaksburg Fortress never saw military action after the reconstruction described above. For cost reasons, the Prussian administration began to demolish parts of the fortress between 1874 and 1900.

In 1885, the Erfurt Beautification Association succeeded in having areas of the grounds of Cyriaksburg Castle made accessible to the public and made available for horticultural planting. Military use of the fortress ended in 1918, and a year later the city of Erfurt reacquired the site from Prussia. In 1950, the garden show "Erfurt blossoms" took place here. In 1961, the "I. International Horticultural Exhibition of the Socialist Countries" (iga) was opened, which also included the grounds of Cyriaksburg Castle, where a horticultural museum was established at the same time. This grew into today's German Horticultural Museum, which has retained its headquarters in the former fortress. The current exhibition "Garden! From Paradise to the Shop Shelf" is currently on display.