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Ossuary Sedlec


Repair of the Ossuary

The main reasons for undertaking the repairs

The main reason for undertaking the repairs is that the building was leaning from the vertical axis. The leaning has reached up to 460 mm maximum deviation of the tower wall from the vertical axis, and has been caused by insufficient load-bearing capacity of the ground on which the whole church is built. According to static calculations, the ground’s load-bearing capacity has been exceeded by up to 2.7 times. This has led to the sinking of the foundation structures – the pillars – 150 to 200 mm. Therefore, the building is leaning because the weight of the towers has shifted the center of gravity of the structure to the west. J. B. Santini tried to solve this problem, too, by adding a vestibule. Another major problem of the building was the dampness of the structures caused by the missing damp-proofing of the load-bearing walls and the floor, as well as by moisture condensation due to frost penetrating the flat terrace roofs.

Assembling the Northwest section of the Skeleton Pyramid
Dismantling the Southwest section of the Skeleton Pyramid
Northern staircase leading to the upper chapel

Originally, i.e. prior to starting the assembling works on the Northwestern skeleton pyramid, the assumption was that the entire construction would be finished by the end of 2022. But given the fact how complicated the construction works are, returning the skeletal remains into the pyramid suffered a significant delay, and even by December 31, 2023, the Northwest pyramid had not yet been completed. In the course of 2023, restorer Tomáš Král and his team were facing numerous problems and issues. The 2nd floor composition, including the cross-vaulted corridor proved to be a very challenging task. However, the way the 4th floor is composed affected the schedule the most. An expert discussion on which shape and form the wooden struts ought to have been supporting the 5th floor, the top of the pyramid delayed the work for several months, as only fragments of the original elements had been preserved. It was as late as at the end of November 2023 when the struts production started according to the documentation agreed upon. During the year of 2023, the second and third floor of the skeletal pyramid was entirely assembled and the restored gold-plated crown was returned. The project of assembling the Northwest section of the Skeleton Pyramid ought to be fully completed in the course of spring 2024.

Dismantling the second skeletal pyramid, i.e. the Southwestern one, commenced in July 2023. Once again, the skeleton pyramid dismantling went on very rapidly. The bones and skulls were stored in transport boxes directly in the ossuary already and taken to an external depository, where the respective preservation work on them was carried out. The skeletons are being cleaned as well as preserved just as it had been done with the remains from the first pyramid that had been dismantled - the bones are rinsed with a water stream and then soaked into a lime water solution, which disinfects and simultaneously reinforces the bones. Finally, the bones are being thoroughly dried, sorted into boxes and stored in a ventilated room.

When the remains had been removed from the lower chapel, the degraded plaster in the vault field was hammered away once pyramid had been dismantled. Subsequently, rescue and archaeological research was carried out here. These works revealed 19 grave pits in total located directly in this field as well as its immediate vicinity, and 17 complete medieval funeral sites were retrieved. Afterwards, the skeletons found here were taken to the Archaeological Institute to be lab-cleaned and to carry out anthropological research, which enabled to determine the age, sex, cause of death and possible diseases.

Apart from the work on the two skeleton pyramids, construction works on the exterior of the All Saints Church and its ossuary continued. In July 2023, the Northern staircase leading to the upper chapel was finally completed. Whereas in the Southern staircase, which had already been completed in 2022 and assembled from the original stairs, new stone steps had to be made from Mrákotín quarry granite (near the town of Jihlava) to be placed into the Northern staircase.

In 2023, almost CZK 17 million were invested into restoring the Sedlec ossuary. The total costs calculated from the start of the works in 2014, amounted to CZK 107 million.

Preparing the field for the skeleton pyramid assembly
Assembling the skeleton pyramid
South staircase to the upper chapel

Three years after the dismantling of the first skeletal pyramid, the pyramid was reassembled in July 2022. However, this was preceded by further construction and preparatory work directly in the north-west field. The original restored wooden structure was the first to be returned to the vault, which was subsequently fitted with a stained glass panel. Subsequently, new stone paving was laid in the field below the pyramid and the original early 18th century Santini "star" paving was restored around the edges of the pyramid.

Already during the construction work on the restoration of the north-west field, the team of experts realised that it was necessary to determine not only the colour scheme of the restored field, but also the overall colour concept of the chapel. For this reason, samples of the plaster layers were taken by the restorers at predetermined locations, followed by a visual and laboratory stratigraphic survey. The results so far show that in the lower part of the chapel, especially in the area of the vault and the walls, the grey shade alternates with the light shade of the stucco decoration. In the plinths, a dark grey shade is applied all around the perimeter. Based on subsequent colour samples carried out and agreed, the north-west bay was painted in March 2022. The final painting of the lower chapel is currently in progress.

In the past years, the general designer ing. Vít Mlázovský and the restorer of the skeletal decoration, Tomáš Král, decided that it was necessary to use the load-bearing inner wooden structure of the pyramid. This construction should provide better stability and reduce the load on the lower layers of the restored pyramid. At the beginning of the year, a very complex production documentation of the new load-bearing wooden structure was completed, which was then manufactured and test-assembled outside the Sedlec ossuary. The assembly of the wooden structure started in April 2022 directly in the field after the dismantled pyramid.

In July, the work on the assembly of the skeletal pyramid was blessed by the parish priest of Sedlec, P. Pavel Tobek, and the process of returning the remains of the first restored pyramid was officially started. The restorer, Tomáš Král, decided to use Plexiglas for the scarfing, which is necessary to preserve the visual plane of the stacked bones, so that he could visually control the appearance of the composition. The plexiglass will then be dismantled after the skulls and bones have been stacked. While the work to assemble the first floor of the pyramid went well, the second floor, with its internal cross vault of bones, was a major challenge for the restorer and his team.

At the same time as the pyramid was being assembled, renovation work was being carried out in the ossuary on the southern staircase leading to the upper chapel. Work to restore the staircase began in early 2022, with the return of the one-piece Baroque staircase treads in April and the staircase opened to visitors in June. Work also continued on the façade of the church's lower chapel, including repairs to the decorative stucco of the oval windows.

Work also continued on the underground extension, located on the level of the lower chapel, where a collector for the electrical wiring was built under the main staircase, into which stainless steel flexible pipes were then installed and cabling routed. In April and May, five light conductors were installed in prepared openings in the ceiling structure of the underground extension. In the southern part of the underground extension, construction work was underway on the lift shaft and in the northern part, the space for the main electrical switchboard was being prepared.

Almost CZK 11 million was invested in the repairs of the ossuary in 2022. The total amount invested since work began is more than 90 million crowns.

Repairs in the vault zone where the disassembled pyramid had been
Repairs in the exterior of the Ossuary

In 2021, due to the drop in funding caused by the worldwide pandemic, we were forced to significantly slow down all Ossuary repairs. Nevertheless, we were still able to make progress on the projects that we began in 2020. From January until the end of September 2021, work was continuing at two locations at once – in the exterior of the Ossuary and in the lower chapel, in the vault zone where the disassembled pyramid had been. Overall, in 2021 we invested about 6 million in the Ossuary repairs. So the total amount invested since 2014 has now reached 80 million CZK.

From January to September, work was taking place in the interior of the lower chapel, in the vault zone where the disassembled pyramid had been. Remnants of the original plaster were cleaned off the walls and the vault, and the masonry was rehabilitated. All spring and summer, the original Santini stucco decorations were being restored. The restoration research and the repairs of the stucco decorations were led by a team of restorers supervised by academically trained painter Tomáš Rafl, Ak. mal. The restoration was undertaken by Karel Navrátil who had also participated in, for example, the stucco repairs in the Pilgrimage Church of Saint John of Nepomuk at Zelená Hora near Žďár nad Sázavou. The moulds that were used in restoring the Santini stucco decorations were created by using prints of the original groin profiles. The stucco decorations in the vault are made of lime mortar on brick core. The challenge was mainly the complexity of the décor and the number of groin crossings.

In 2021 we also renovated the exterior stairs at the entrance to the lower chapel, we began renovating the southern Baroque stairs leading to the upper chapel, and we built new exterior stairs on the northwest side of the Ossuary. The most challenging of these projects, in terms of both planning and implementation, has been the southern Baroque stairs leading to the upper chapel. Construction on these stairs began in September 2021, and the stairs will be open to visitors in the summer of 2022.

During all of spring and summer, work was also progressing on the bookshop ceiling which is architecturally as well as structurally unique – the bookshop is the underground addition that is being built at the level of the lower chapel. We decided to build this bookshop back in 2017, when the church masonry was being damp-proofed and the Ossuary was surrounded by a trench. Since then, we have worked on the bookshop continuously, with the goal to open this sales and exhibit space to visitors by 2025. Because the bookshop is underground, the ceiling will also be the roof. And so it was very important that the ceiling be properly insulated. Above the ceiling, which is made of reinforced concrete, was built a structure consisting of layers of waterproofing and thermoproofing, including a sophisticated rainwater drainage system for the whole bookshop area. The structure is surfaced with a layer of crushed-stone pavement. Additionally, the Lanostav s.r.o. company built low support walls with outside vents for the bookshop’s ventilation system.

2019 – 2020
The dismantling of the pyramid, construction of the bookshop, and structural stabilization of the building

The dismantling of the pyramid was started in January 2019 by taking apart the polychrome wooden crown. First, the pyramid was fully documented, photographed and mapped. The dismantling of the pyramid was done storey by storey, from January 2019 to the end of March 2019. The bones were put in carton boxes and taken to the restorer’s workshop. Altogether, 1,500 boxes were filled with bones. Inside the pyramid, there were 6 cubic meters of construction debris which smoothed out the unevenness and helped to strengthen the pyramid. From April 2019 to October 2019, the bones were cleaned and preserved in the restorer’s workshop. Various cleaning options were tested, including, for example, washers, but in the end the bones were washed manually, with water under gentle pressure and using nylon brushes. Then the bones were disinfected and stabilized in lime water, and dried by large blowers hanging above the multi-tier racks. After drying, the bones were placed back into boxes and prepared for transportation to the Ossuary. The process of reassembling the pyramid is now under intensive consideration, with the goal to start putting the pyramid back together in the winter of 2020/2021. Under the pyramid, the floor was made of bricks, and around it, there are Santini’s original two-coloured (black-red) diamond-shaped floor tiles. The individual segments are composed into a complex geometric figure with the effect of a flower and also of cubes stacked on top of each other. During the whole of 2019, intensive work was done on the emerging space in the front part of the original trench, in the so-called “bookshop”. The development of this space had been approved ear-lier, when various possible ways of relieving the constantly overcrowded Ossuary entrance were be-ing examined. At that time, a trench was dug around the church for masonry rehabilitation. And, thanks to the unexpected discovery of an historical entrance into the lower chapel, the idea was conceived to use this entrance and connect the original lower chapel with a new addition which would house a souvenir shop, a small exposition, and facilities for guides. Architects Filip Kosek and Jan Říčný from the Prague architecture studio RCNKSK were asked to design the newly created space of the “bookshop”. The interior of this addition is supposed to evoke as much as possible the atmos-phere of being underground and to remind visitors that this place is a former graveyard. Therefore, it was agreed that the final coat of the interior perimeter walls would be done using the rammed earth technology. However, to date there is no one in the Czech Republic who would have experience with this technology, and so we approached Austrian expert Hanno Burtschner, and during the au-tumn months, earth ramming was tested right in the space of the emerging addition. Prior to this testing, the foundation for the addition’s perimeter wall was laid, and then a supporting wall made of permanent formwork blocks was built, including quality damp-proofing. The rammed earth tech-nology itself was applied using the same formwork that is used for concrete. The earth mixture is composed of soil, sand, fine and coarse gravel, clay, and an appropriate amount of water. The mixed materials are then poured into the formwork and rammed, either manually or by a pneumatic ham-mer. This process is repeated several times. After the formwork is removed and its imprint smoothed out, the wall dries out and gains its final compactness. The individual layers of the rammed materials form horizontal lines that have a strong aesthetic effect. The ramming of the wall at the Ossuary took five weeks (April 2020 – May 2020). Experts had to prepare 14 cubic meters of materials. The final length of the wall is 27 m and its height is 2.2 m, so altogether it covers approximately an area of 60 square meters. The wall was rammed in layers of 9 cm which were rammed down to 5 cm. The wall consists of 46 layers. In the summer of 2020, inten-sive work was also done on the ceiling of the addition which will be made of concrete but will be shaped into “bellies”. The moulds for these “bellies” were made of mortar, clay, and sand, and each “belly” is an original piece hand-made by sculptors. By the end of 2020, damp-proofing is to be ap-plied on the ceiling, and then the finishing of the crushed-stone walkway around the whole perimeter of the Ossuary is to be done. Together with the construction work in the “bookshop”, we continued with renovating the interior of the Ossuary’s lower chapel, with special attention given to the chapel’s problematic structural stability. Strengthening all of the pillars was suggested, using the method of widening the existing foundation structure by underpinning made of worked stone blocks with mortar of compressive strength 5MPa. The existing foundation of the northwest pillar was gradually, section by section, underpinned all around by a new foundation under the existing footing base. In December 2019 and the second part of January 2020, carpenter’s lagging was installed in four vault zones of the north-west pillar, and during February and April, the northwest pillar was underpinned. The plan view of the trench was a square with sides of almost 5 m. The depth of the trench was approximately 1.5. m. The foundation is underpinned by four rows of worked stone blocks and fastened by stainless pull pins. After the underpinning was finished, the foundation was covered with a mixture of gravel and dug-up loess loam, foam glass was added in the upper layer, and everything was thoroughly com-pacted.

2017 – 2018
Damp-proofing of the church masonry, rescue archaeology research, and continuing work in the interior

In 2017 and 2018, damp-proofing of the Ossuary masonry was done by creating drainage and venti-lation channels around the perimeter of the whole building. We also started to repair the façade of the lower chapel of the Ossuary. The exposed perimeter masonry, mostly made of stone, was recon-structed, including filling in of the joints with mortar, re-masoning and repairing the load-bearing pillars, and finishing the openings of the Baroque windows. The windows were removed and refur-bished, together with restoring the stained glass, and then they were re-fitted into the prepared openings. Damp-proofing construction work, which exposed the Ossuary foundations down to the level of the footing base (2,5-3 m), were preceded by rescue archaeological research. During this research, all deposits and all evidence of burials were removed within a 2-metre belt along the whole perimeter of the Ossuary. This represents the largest sample of its kind that has been examined in Europe; the findings contain information about the Mediaeval population that occupied Kutná Hora and the sur-rounding area. The uncovering of the cemetery brought several surprises. It was originally presup-posed that burials next to the church did not begin until after the church was built. However, several tens of graves were disturbed during the church construction, which means that the graves were older than the church. Before the Ossuary was built, an older structure stood nearby. Corner rem-nants and one wall of this structure were also found. The rest of this structure lies under the current cemetery and is not open for research. Rescue archaeological research at the Ossuary was started on 30 May, 2016, and continued until 16 August, 2018 (from the originally planned four months it was extended to 2 years and three months). The number of excavated skeletons was 1,817, and 32 mass graves were discovered. One part of the mass graves was dug in 1318 for victims of the Great Famine, and the other for victims of the Plague in 1348-1350. Some of the mass graves disturb each other, and so we can unequivocally date four of them to 1318 and another seven to 1348-1350. In 2018, some of the repairs moved into the interior of the Ossuary, where a working space for restoring the bone pyramid was created. A temporary entrance was made in the northern Gothic window and a wooden structure with a staircase was built, which enabled construction work and transportation of bone remains to proceed. The preparations for the interior repair included assembling a temporary dust-proof wooden partition with a photo mural and “viewing windows” to minimize the impact of the work in progress on the visitors’ experience of the Ossuary tour and to offer the visitors some satisfaction.

2014 – 2016
Repairing the terraces, the trusses, and the chapel roof, and restoring the bone ornaments in the interior of the lower chapel

The repair of the terraces (2015-2016) included covering them by a temporary roof and com-pletely removing all the layers, down to the reverse side of the stone vault. The vault was recon-structed and structurally secured by pull pins, and the damaged parts of the masonry were redone, together with the perimeter wall. At the same time, the plinth section of the church was restored, and a drain was fitted in the newly built underpinning. The drain is covered by a lead-lined trough which allows the terrace to be drained by vents in the wall. All this was covered by a drainage layer of aggregate and sand, in which sandstone pavement was embedded. This new composition of the terraces has eliminated the condensation caused by frost penetration and, moreover, it has allowed us to open the terraces to the public. The impetus to repairs of the hanging decorations in the interior of the lower chapel was the fall of one of the pendants made of thigh bones. Subsequent research confirmed our concern: the an-choring components and steel wires had rusted to the point of starting to fail. It was a ticking bomb waiting to explode. The Parish and restorer Tomáš Král prepared a schedule of repairs and still in the same year (2015), the most seriously damaged components started to be restored. The restoration process is as follows: detailed photo-documentation is conducted prior to taking down the pendant, individual parts are labeled, and the pendant is removed, packed, and sent to the restorer’s work-shop. In the workshop, each pendant is blow-cleaned by pressurized air, taken apart, and each part is mechanically cleaned by nylon brushes, disinfected, and stabilized in lime water. Then the individ-ual parts are fastened to new anchoring components, and the old anchor pins in the walls are re-placed by new, stainless steel ones. The whole process is done in a way that will make dismantling the pendants in the future easier. In the final step, the pendants are fastened to the prepared an-chors. Complicating the work, because the chapel continues to be open to visitors, the restoration must be carried out after closing time, in the evening and at night. Moreover, dismantling too many pendants at once would leave nothing for the visitors to see. In 2016, after the most seriously damaged pendants were repaired, we decided to restore the chan-delier. During the dismantling of the chandelier, we discovered that the chandelier’s anchor was only wedged in the vault by a no-longer-functional oak wedge and a piece of lead. The chandelier is com-posed of a wooden vertical stem, four circular storeys, and cradling supported by wrought-iron strips. The surface of this wooden frame is covered in bone decorations fastened to the frame with spikes and screws. The width of the chandelier frame is 1,915 mm, the height of the frame is 2,086 mm, and the total weight of the chandelier is approximately 150 kg. There are 1,041 bones in the chandelier decorations.

Prior to 2014

During this time, important preparations were underway – exploratory bore holes in both the interior and the exterior, and also negotiations regarding planning, scheduling, sequence of projects, and financing of the complete and complex repairs. It was decided to finance the whole construction from our own resources – that is, from the income from tourism, without subsidies, grants, and funds. We made this decision because it gave us a certain kind of freedom to conduct the repairs “our own way”, without unnecessary paperwork and tenders, and with suppliers of our own choosing. Further, we needed to approach the design and realization teams and agree on long-term coopera-tion. Ing. Vít Mlázovský was named the chief project designer and Lanostav s. r. o. became the general contracting company.