From the abandoned castle to bridgehead fort: archaeological investigations in the Stopfenreuther Au area

“No one crosses the border unobserved” - what sounds like an agent thriller today was a reality on the Roman Danube Limes. However, the Roman border fortifications were not rigid defenses, but a flexible control and communication system. They monitored border traffic, levied customs duties and prevented minor incursions. In addition to watchtowers and large legionary camps, forts and bridgeheads played a central role: strategically erected at river crossings, they secured military operations and controlled important trade routes.

But what exactly is a bridgehead fort? It is a military installation that served to secure a river crossing. As a rule, such a fort was built on the opposite side of a border river in order to control a strategically important bridge. From there, Roman troops were able to monitor not only the river crossing but also the neighboring areas. On the Danube Limes in particular, such installations were an integral part of Roman border security and served to control trade routes and troop movements.

In the fall of 2024, the first archaeological evidence of a Roman bridgehead fort on Austrian soil was found in the Stopfenreuther Au. Comparable sites are only known from Slovakia, in particular the Iža-Leányvár fort opposite Brigetio, where the remains of a Roman Danube bridge were recently discovered.

Plan of the 1898 excavation under the direction of Maximilian von Groller-Mildensee (see Groller-Mildensee 1900) 

As early as 1850, Eduard von Sacken reported on the remains of walls in the Stopfenreuther Au that were still visible at the time and interpreted them as a Roman bridgehead. According to him, the Amber Road may have crossed the Danube here, with brick stamps from legio XV Apollinaris supporting his theory. However, later investigations around 1900 by the Limes Commission of the Imperial Academy of Sciences under the direction of Maximilian von Groller were hampered by flooding. His plan documents a rounded corner of the wall with adjoining structures, but both its function and exact dating remained unclear.

Until around 1860, the walls were visible on the surface and were known in the region as the Hungerstein or Durstkugel. The complex was mentioned in documents as Veste Stopfenreuth or Ödes Schloss. Last year, investigations began again at this site: In February 2024, GeoSphere Austria carried out geophysical investigations, although these were made more difficult due to the dense vegetation. Archaeological excavations began in September 2024.

Remains of the fort walls at low water level in 1908 (Wikimedia Commons)

In the fall of 2024, the Austrian Archaeological Institute of the Austrian Academy of Sciences and the state of Lower Austria carried out a research excavation in the Stopfenreuther Au - in close cooperation with the Donauauen National Park and the Federal Monuments Office. The aim was to gain new insights into the Roman fortification at the “Öden Schloss”. The excavations brought to light excellently preserved wall structures of a Roman fort, in places over 2.5 m high. Particularly striking was the northern, rounded corner of the fort with an internal corner tower and adjoining walls. In addition, an upstream ditch system with at least one ditch was uncovered.

The investigations revealed two construction phases: the first phase dates to the time of the Marcomannic Wars (166-180 AD), the second to the second half of the 3rd century, when it was possibly rebuilt under Emperor Gallienus. However, the site was abandoned soon afterwards. Archaeological finds from the late 4th century also provide evidence of renewed activity on the site.

Model of the excavation area uncovered in 2024 (Modell: 2024 H. Wraunek, Land NÖ)

The Austrian section of the Danube Limes was inscribed on the UNESCO World Heritage List in 2021 as part of the transnational World Heritage Site “Frontiers of the Roman Empire - Danube Limes (Western Section)”. This inscription underlines the importance of the Roman border fortifications as cultural heritage, which not only represented a military demarcation but also promoted cultural exchange along the Danube.

The fort in Stopfenreuth, today located on the left bank of the Danube, is therefore another World Heritage Site that marked a strategically important point on the Amber Road, which led south from the Baltic to the Roman Empire. The military installations along the Danube were not only used for defense, but also to control trade and passenger traffic. Customs duties could be levied and export bans enforced. Stopfenreuth thus played a central role in the military security of this section of the border. 

Backwater of the Danube near Stopfenreuth (N. Kirchengast 2024)

The renewed archaeological investigations last year provided evidence of a Roman bridgehead fort for the first time in Austria. Further analysis of the finds and features in 2025 should provide new insights into the chronology of the site, the development of the course of the Danube and the function of the fort in the context of Roman border defense.

Further Reading: 

M. von Groller-Mildensee, Das „Öde Schloß“ an der Donau, Der Römische Limes in Österreich 1 (Wien 1900), S. 87–92.

H. G. Walter, Römische Funde in Stopfenreuth, Pro Austria Romana 7, 1957, S. 23.

K. Genser, Der österreichische Donaulimes in der Römerzeit. Ein Forschungsbericht, Der römische Limes in Österreich 33 (Wien 1989), S. 661–663.