Conservation of the Romanesque chapel of St. John the Baptist in Petronell Carnuntum the Lower Austria hidden jewel

By Eva Videnska

In the small village of Petronell-Carnuntum, Austria, one can observe a Romanesque round-chapel calmly resting between low fortification walls situated on a small hill. Built in the late medieval era of the 12th century, the chapel is believed to have originally served as a Romanesque baptistry due to the presence of a tympanum bas-relief depicting Jesus standing in the river Jordan. Jesus is placed in the middle of the composition with St. John the Baptist on the left side baptising him, while on the right side an angel holds Jesus’ garment. The scene is overlooked by the Holy Spirit from above in the form of a dove. Over the centuries, the building has served as a church, a horse stable and a chapel.  Since 1729, when the tomb was added to the building, it has served as a noble mausoleum for the oldest extant Austrian family, Abensperg und Traun. The private mausoleum is currently undergoing restoration and conservation of the exterior walls from 2022 until 2024. This place has an excellent genius loci in part because this Christian building is standing on a Roman burial ground of the ancient city Carnuntum, capital of province Upper Panonia (after 1st century AD) belonging to Roman Empire. Once this conservation campaign is finished, the mausoleum can serve as a chapel once again.

Beyond the changing historical functions of this building, another of its interesting stories is that of its past renovation and restoration campaigns linked to the historical context. During more than 800 years, the building underwent many major and minor renovation and restoration campaigns which coincided with a great deal of vivid history. Major damage to the building’s stability occurred when it suffered an explosion from the inside; today you can see large vertical cracks in the main part of the building—a memento of the Ottoman invasions. Pichler (1999) assumes that the original roof was made of stone and had collapsed or had become so damaged that it had to be removed and was replaced with a baroque conical shingle wooden roof. The cracks in the exterior walls were later filled with bricks and stones. He also notes that the building was in great disrepair around 1569, based on a document originating from Schlossarchiv Petronell, dated 17 May 1569, which describes the very poor state of the round chapel as reported by Sir Andreas Eberhardt Rauber from Thalberg and Weineck.

Gerd Pichler, in Studien zur Baugeschichte der St. Johannes-Kirche in Petronell und Ihres Vorgangerbaues, describes the history of the surrounding land, from ancient times to the 20th century, focusing in particular on the detailed description of the Petronell’s round chapel and its renovations, restorations and research.

We were able to observe, as it were, under our magnifying glass, the last restoration campaign which dates back to the 1950s. This last campaign is one of the main reasons why the chapel is in need of restoration today. Seventy years ago, gaps and areas of missing stone were filled with cement. In addition, a significant number of whole stone elements are missing from the blind arches lining the nave, and many of the floral capitals and other nature-depicting decorations were significantly weathered or damaged. There is a dentil moulding lining the upper edge of the wall; a small segment of it is exposed right above the portal, but the rest is covered with mortar formed to look like a cornice.

The current conservation campaign of the exterior started in 2019 with an exemplary restoration of the Romanesque portal. Then the Slovak-Austrian team took over the work in summer 2022 which will continue to summer 2024. This latter stage has focused on the exterior walls of the building which suffered mainly from weathering of the stone architecture and from the 1950s treatment.

There were many missing decorative stone elements; these losses may be creating a disproportionate distribution of pressure on the building in certain areas.  Upon visiting the site, Jindrich Vidensky, a Slovakian geologist and palaeontologist, observed that the uneven weathering of the stones is caused by different densities of limestone caused by the presence of a clay-loam compound in the limestone which differs from one stone to another. The presence of this compound makes the stone particularly susceptible to weathering, especially those stones which are fine-grained and do not possess attributes, such as a strong layered structure, that the majority of organogenic limestone has. Macro-fossils in organogenic limestone occurs very rarely.

He adds that in Imrich Sladek’s 2021 paper, Geologicky vyvoj a stavba Bratislavy a okolia (Devinske Karpaty a Hainburske vrchy)--which can be translated to Geological evolution and building of Bratislava and surroundings (Devin Carpathians and Hainburg Hills)—Sladek mentions three historical stone quarries in the area between Hundsheim and Hainburg, namely Hundsheimer Berg hill and Pfaffenberg hill.

These limestones are rich in fossils (containing bivalves, mosses, algae, gastropods, etc.) and they were created in the geological Miocene Epoch of the Neogene Period (23 million to 5.3 million years ago). Vidensky assumes that stones for the round chapel could have originated from this quarry. Also, we assume that spolia are present from the Roman era and were used in later renovations.

In regards to the use of cement in the 1950s restoration, we observed a heavy patina of lichens and mosses accumulating on the adjacent stone. The cement was simultaneously too hard, in contrast to the original stone, and prone to holding in moisture, which caused this damaging growth, speeding up the weathering of the original stone. After long sessions of manually removing cement from the monument, followed by a gentle water pressure cleaning, we slowly brought the building back from the dark noble tomb to the time when it served as a baptistery.

The stones were then impregnated with the stone strengthener Remmers KSE100 (silicic acid ester base). During the winter 2022/2023, missing stone decorations were carved in the nearby open-air stone workshop of Bernadette Klasz and L. Hasto. The stones originated from the outdoor lapidarium of the noble family, having a very similar composition to the original stones. A mineral stone replacement mortar by Remmers was used to fill other losses in the exterior walls, tinted with a small portion of different coloured and shaped sand and stones.

In addition to serving as a religious building, the round-chapel also holds a strategic viewpoint which could have helped to predict and protect from potential attacks, which so often occurred in this region. The most impressive finding so far during the current conservation campaign of the Slovak-Austrian team occurred while working to remove cement and biological growth from the upper walls. The team uncovered the original roof drainage system, which at some point had been filled with mortar and bricks. In an effort to understand the original structure, a hypothetical system was drawn by architect Milos Dunaj. These sketches suggest that rainwater could have been collected via a small canal around the outer edges of the original stone roof. The water could have then drained through four L-shaped water gutters built inside of the exterior wall, leading to an extended U-shaped stone spout. The team found long stones (approximately 70 cm long) pushed inside the gutters and covered with mortar and bricks, with one gutter transformed into an air well, rendering them useless for their original purpose. These four stone gutters were evenly distributed around the outer wall of the nave. The outer round shape of the doom-like roof would have been accessible and could have served as a viewpoint for guarding the area and protection when under attack. The true nature of the original roof will perhaps remain a mystery, at least for now.

The inner part of the mausoleum is composed of a round nave, with walls approximately 2.5 m thick, and a semicircular apse with thinner walls around 9 m thick, boasting a secondary vault in the apse and brick flooring with gravestones situated under a triumphal arch around a built altar. The originally painted decorations on the walls are almost completely gone; only the consecration crosses remain, hardly visible and reminiscent of painted fragments on the triumphal arch from the apsidal side. The inner stones in the nave have many mason markers. On the outer and inner walls of the building, there are mason markers positioned in the middle of the stones. I have found at least five types (on exterior walls), but their readability is slowly vanishing due to weathering. Pichler included drawings of eight different markers, likely from the exterior and interior walls. Interestingly, some of the stone markers on the exterior walls are located in similar spots (for example, most of the “O‘’ signs are located around the three-quarter engaged columns of outer walls). Could it be possible that these stone markers also served as locators, to match the curved walls of ashlar masonry? 

During the summer of 2024, the Austrian-Slovak group of restorers (Bernadette Klasz, Nikita Jurkowitz, Lubomir Hasto along with Alexandra Klammer) will continue taking care of the exterior walls of the apse. They will be happy to guide any visitor.

Author Bio: Eva Videnska, M.A., M.F.A. graduated from The Academy of Fine Arts and Design in Bratislava (easel and panel paintings conservation and restoration) and from the University of Constantine the Philosopher Nitra (fine arts and aesthetics). She is a private conservator and a teacher of conservation who grew up under the Romanesque Church of St. Michael The Archangel in Dražovce, Slovakia.

You can read this article in Slovak on the IIC Community Platform! Click HERE.

Read the entire December-January 2024 issue of "News in Conservation", which you can access from the IIC homepage.