Vienna cooling network expansion reveals Roman remains

Vienna’s district cooling network is expanding while construction work uncovers archaeological remains from several periods, ORF reported. The city plans to invest 100 million euros in the network over the coming years.

New district cooling lines require considerably deeper excavations than water and sewer projects, creating opportunities for city archaeologists to investigate historical layers beneath Vienna’s streets. The network currently supplies around 300 buildings.

Among the discoveries is a large Roman basement at Bauernmarkt that was probably a prison, known as a carcer. Evidence of Roman prisons is rare. According to Kristina Adler-Wölfl, head of Vienna’s city archaeology department, the find may indicate that the building was no longer used solely for military purposes in late antiquity.

By that period, Vindobona, the Roman legionary camp beneath Vienna’s first district, had become a fortified city with both military and civilian uses.

Archaeologists also found ninth- to eleventh-century graves at Petersplatz, parts of a Roman camp gate at the corner of Graben and Naglergasse, and a column base about 2.8 metres below Wildpretmarkt. The column base suggests that travellers on the Roman main road were protected from sun and rain by a columned structure.

Another current excavation concerns a Roman road beneath the Kohlmarkt. It ran west from the southern camp gate, known as the porta decumana, via present-day Michaeler Platz towards Cetium, now St. Pölten. Archaeologists have documented sections of the road, drainage channels and material from the fourth and fifth centuries.

Construction trenches provide only brief opportunities to examine the past. Archaeological teams are involved during the planning stages, photograph and survey soil profiles and layers, and recover and study artefacts. Modern three-dimensional recordings are intended to make the documentation faster and more precise.

Vienna’s utility company Wiener Netze coordinates its pipeline planning with the city archaeology department at an early stage. This allows teams to assess which areas are likely to be archaeologically significant, how many archaeologists a project may require and how long investigations could take. If discoveries are made, they can be recovered and examined while construction crews carry out other work.

Some finds remain in place. At Bauernmarkt, the district cooling route was diverted around the late antique basement window believed to belong to the prison.

For the city archaeology department, the network expansion offers a rare chance to examine deeper historical layers in the densely built first district. The excavations are adding pieces to the overall picture of the Roman legionary camp, although details about its internal layout and full extent are still missing.

Wien Energie plans to expand the district cooling network substantially over the next five years and will invest 100 million euros in the work.