As if it had been in operation yesterday: Archaeologists have discovered surprisingly well-preserved underfloor heating from Roman times under a street in Bonn. Under the floor, brick pillars still form the cavities where warm air once circulated. According to further findings, this so-called hypocaust apparently once warmed a stately building. It may have been a bathhouse near the Castra Bonnensis legionary camp, experts say.
Water pipes had to be replaced and new pipes laid: The current history of the find on Pfarrer-Merck-Strasse in the Friesdorf district of Bonn began with construction work. Since this was an area for which there were already indications of archaeological monuments, the work was accompanied by archaeologists from the company "Fundort" and the Office for the Preservation of Archaeological Monuments in the Rhineland (LVR-ABR). As it turns out, it was worth it: an exciting structure actually appeared at the bottom of an uncovered cable ditch. It was a flat surface that turned out to be an antique floor. A narrow opening in the Roman floor revealed that there was a cavity beneath the surface. The archaeologists then used video cameras to explore it.
Without debris and burglaries
What was revealed caused astonishment. Actually, Roman buildings with underfloor heating in the Rhineland are not that unusual. "But usually the floor collapsed or the cavity was otherwise filled," says Jens Berthold from the LVR-ABR. In this case, however, the structures of the hypocaust under the ancient floor were still completely intact. "This finding is something special," emphasizes Berthold. Specifically, it turned out that the screed floor still rests on 65 centimeter high brick columns that are set up in regular rows on a sub-floor. In addition, cover bricks were installed between the screed floor and the columns, which served to store heat. As the experts explain, the heat generated by a fireplace on the western side of the room could circulate between the columns.
In addition to the room with underfloor heating, the foundations of two other rooms also came to light and the archaeologists were able to document a section of an ancient water pipe. They also discovered many fragments of painted wall plaster, which testify to the apparently elaborate interior design of the rooms. Investigations using georadar also showed that it must have been an elegant facility. With this method it is possible to identify structures in the ground without the need for excavation. As the team reports, structures on the radar image reflected that the underfloor heating was probably once located under a room with an apse. However, the full dimensions of the room and heating system remain unclear, as structures on the surface limit the ability to measure, the archaeologists say.
Was there a bathhouse here?
Based on the remains of walls that had already been discovered in the 19th century, it had already been assumed that a stately building once stood in the area where the finds are now. A Roman country estate – a so-called villa rustica – came into question. However, the new findings now make another possibility seem plausible: "Perhaps we are also dealing with a small bathing facility here, south of the legionary camp," says Berthold. In order to be able to say more precisely, however, the results of the excavation must first be evaluated more precisely, say the experts.
Although the heating structure has remained unfilled for so long, the archaeologists now want to change that: the cavities are to be flooded with so-called liquid soil. "This should not only prevent the ground from sinking, but above all preserve this special finding," explains Tanja Baumgart from the LVR-ABR. By using a special mixture, the liquid soil becomes solid, but can be easily removed at any time. In this way, the archaeological monument is protected from damage caused by the collapse of the cavity and is then available for later archaeological investigations, the archaeologists say.
Source: Rhineland Regional Council