Archaeologists Discover a Roman Castellum on the Banks of the Danube, the First Found in Austria

For the first time, an archaeological investigation has conclusively documented the existence of a brückenkopfkastell—a Roman auxiliary outpost castle erected at a strategic river crossing point—on Austrian soil.

The discovery, made by a joint team from the Archaeological Institute of the Austrian Academy of Sciences (ÖAW) and the Carnuntum Archaeological Park, provides new insights into the military and logistical role played by the Lower Austria region during Roman rule, particularly regarding the control of the Danube and the monitoring of the trade route known as the Bernsteinstraße or “Amber Road.”

The discovery took place in the floodplains of the Danube, specifically in the Hainburger Au, an area near the historic Roman city of Carnuntum. There, in a location previously known as Ödes Schloss—literally, “desolate castle”—archaeologists uncovered notable masonry structures in excellent condition, some of them over 2.6 meters tall. These architectural remains confirm suspicions dating back to the mid-19th century that the site had housed a fortified Roman military position.

roman castellum danube austria — Aerial view of the Roman city of Carnuntum, where today you can visit completely reconstructed and functional buildings from the Roman period. Credit: Römerstadt Carnuntum

As explained by archaeologist Christian Gugl, head of the Roman provinces research group at the ÖAW, the site was already examined around 1850 due to the presence of visible surface walls. The brick stamps found at that time were interpreted as signs of a Roman installation, though only now, thanks to modern archaeological methods, has it been possible to confirm its nature as a river-control castellum.

This type of structure had a specific role within the Roman defensive system: usually built on the opposite bank of a frontier river, the brückenkopfkastelle were designed to protect crossing points and ensure the monitoring of movements in the surrounding territory. In the case of Carnuntum, although there is no evidence of a permanent bridge during Roman times, it is known that ferry services operated in the area up to the 17th and 18th centuries. This does not diminish the importance of the discovered fortification but rather highlights its role as a logistical hub and surveillance post at a key frontier of the Empire.

The historical significance of the finding has been emphasized by various authorities. The governor of Lower Austria, Johanna Mikl-Leitner, highlighted the symbolic value of this new archaeological evidence, which not only confirms Carnuntum’s role as a central node in the Empire’s communications network but also offers an enriched perspective on regional history. In her words, understanding the function this region played in the past enables more informed and sustainable decisions for the future.

Meanwhile, ÖAW president Heinz Faßmann regarded the discovery as a new path for bringing ancient history closer to the general public. He noted that Carnuntum is an emblematic place where the Roman era is not only studied but also experienced through faithful architectural reconstructions and high-level educational activities.

It is worth noting that, until now, the only known structure of this kind along the Danube Limes was the castellum of Iža-Leányvár, in present-day Slovakia. The inclusion of the Austrian site in this context adds a significant chapter to the understanding of the Roman frontier system, which was declared a UNESCO World Heritage Site in 2021.

The analysis of the materials found—including coins, ceramic fragments, small bronze objects, and bricks stamped with the marks of Legions XIV and XV—has made it possible to date the construction of the fort in two distinct phases. The first, around the year 170 AD, during the reign of Marcus Aurelius and in the context of the Marcomannic Wars; the second, around 260 AD, under Emperor Gallienus, at a time of transformation and the progressive weakening of the Roman presence in the area.

Beyond the historical and architectural value of the discovery, the research has offered an opportunity to deepen the study of the Danube’s riverbed evolution. Given the scarcity of cartographic records before the 16th century, archaeologists, in collaboration with specialists from the University of Natural Resources and Life Sciences (BOKU) and the University of Vienna, collected sediment samples in order to reconstruct river dynamics and provide data for the study of the landscape in the context of the Anthropocene.

The excavations, completed in 2024 with the support of the Federal Forests and in coordination with the Donauauen National Park, adhered to legal requirements for environmental conservation. Nevertheless, the scientific analysis phase is still ongoing, with the expectation that the results will decisively contribute to redrawing the historical-military map of northeastern Austria in the time of the Roman Empire.