The antechamber of the Mithraeum

SÍLVIA LLOBET

Conservation and restoration work on the antechamber of the Mithraeum

THE MITHRAEUM IS A LARGE BUILDING

constructed between the 2ND and 3RD centuries and divided into different spaces. First, there is an entrance corridor followed by an antechamber meant as a reception area and place to prepare the ritual banquet. This antechamber leads to the cave where the initiation rites and banquet were held, which reflected the architectural features of these spaces of worship: rectangular layout, central corridor and two benches built into the walls where participants could recline while eating. Lastly was the three-part worship room, only the foundations of which still remain, although it must have been presided over by an image of Mithra’s ritual killing of the bull.

Background

Most of the structures of the Mithraeum were excavated between 2004 and 2005, and since then several urgent campaigns have been conducted, primarily focused on bevelling the wall claddings of the antechamber and the benches in the cave. Given the endangerment of conserving the remains, in 2019 the Centre for the Restoration of Artefacts of Catalonia (CRBMC) and the National Archaeological Museum of Tarragona (MNAT) decided to undertake the conservation and restoration of this sector via the antechamber.

The antechamber, the Mithraeum’s reception area

This is a trapezoidal area measuring 29 m2. The northwest wall was the facade visible from the portico, and it was built with a baseboard of irregular stones attached with clay mortar and raised with sun-dried brick, then covered with a mural both inside and outside. The remains of the wall that is still conserved inside show a baseboard with a white background and red stripes that delimit a series of panels.

The northeast wall, which was only visible from the inside, is also amidst pillars made of more regular stones attached with lime mortar. The remains of the murals also have a white baseboard and red stripes which delimit panels and inter-panels with an ochre background. Finally, a bench around 60 cm wide runs along the walls, although it is currently only conserved across from the door leading to the cave, and wall claddings are conserved which largely echo the decoration of the others.

State of conservation

The antechamber’s overall state of conservation was poor. There were numerous agents of deterioration, as the structures are exposed to climatic agents, most importantly rainwater. The site stretches along the western slope of Cap Roig, which projects westward to create a regular platform, where the central core of the villa was located. It spread along a slope until connecting with the southern baths via a ambulatio, to the south of which the Mithraeum was built. The Mithraeum bears the impact of the water runoff, which causes scouring problems on the claddings and the deterioration of the walls’ foundation.

The lack of a roof over the structures also led to the development of biocolonisation, such as the growth of plants on top, microorganisms and the damage caused by the presence of insects and other arthropods. Likewise, the exposure to ultraviolet radiation affects the conservation of the murals.

The walls, especially those built with clay mortar, had structural problems such as the loss of the mortar and the shift and flaking of some elements. Problems of fissures, flaking, gaps and separations between layers and disaggregation were found on the walls.

On the claddings of the Mithraeum, an accreted layer was identified which was analysed in

Orthoimages of the northwest wall of the antechamber of the Mithraeum. The upper ones show the wall on the inside before and after the treatment. The lower ones show the state of the outside after the treatment. Photo: Jaime Salguero

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Orthoimages of the northeast wall of the antechamber of the Mithraeum before and after the treatment. Photo: Jaime Salguero

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Close-ups of the state of conservation of the northeast wall with the remains of murals, and a view of the northwest on the outside. The image on the right shows the state of the southern facade and the bench in the entrance to the cave. Photo: Sílvia Llobet

the CRBMC’s physiochemical analysis laboratory. According to the results, there was calcium carbonate, a clayey compound and other aluminosilicates (soil). At the same time, soluble salts were found on all the elements, which were also analysed and identified as lime, calcium carbonate and sodium sulphate.

Conservation and restoration of the antechamber

The work got underway with photogrammetric documentation of the state of conservation, studying the damages and mapping the site.

The first conservation process was a biocide treatment, following by a mechanical cleaning of the walls focused on eliminating the plants and soil deposits, a laborious task on the northwest due to the large amount of construction and decorative materials that were above and around the structure, which had to be collected and packed. The soluble salts were also rubbed off.

Before consolidating the walls, the different original mortars were studied and the most appropriate materials to make the restoration mortars were chosen, in this case hydraulic lime and with solids that include cleaned river sand, coarse sand, pebbles and crushed pottery. All the stone elements that were added for to reinforce the structure and improve the interpretation of the complex and all the stones attached were placed over an internal fiberglass net as a separation material. Mortar was added to all the lost joint mortar and the deteriorated lower parts of the walls.

The wall claddings were cleaned, the soluble salts and microorganisms were removed from them and they were reattached to the wall with wet lime mortar and crushed pottery. Wet lime was used to make the mortars for bevelling and replacement, and the dry materials were river sand, coarse sand and pebbles for the preparatory layers, while finer solid materials were used

Close-up of the replacement of lost mortar on the outer northwest wall. Photo: Sílvia Llobet

for the upper layer, such as marble powder different tones.

The stone elements in the entrance zones and door thresholds were treated with mechanical cleaning and biocide treatments, and the small flakes were stabilised and all the cracks, joints and deteriorated lower parts were fixed.

Finally, the internal circulation level of the antechamber was restored to avoid the accumulation and improper circulation of rainwater, while also protecting the lower parts of the walls and improving their presentation. A polypropylene cloth covered with up to 50 cm of crushed stone was installed, attached with a flexible PCV edge at the threshold to the cave.

Future proposals

The restoration work started in the antechamber is scheduled to continue in the other structures still conserved in the Mithraeum in order to guarantee the future integrity of the space of worship. Additionally, since 2019, the CRBMC has been working on drawing up the Preventative Conservation Plan of the Villa of Els Munts, which should include preventative conservation projects, their scheduling and risks assessments and the measures to correct them. Without all of this, it will be very difficult to preserve all the structures in this unique complex that are still conserved.

Close-up of the consolidation of internal wall claddings. Photo: Sílvia Llobet

DETAILS

GENERIC CLASSIFICATION: archaeological and palaeontological material | OBJECT: mural painting | MATERIAL/TECHNIQUE: lime mortar and stone | DESCRIPTION: side walls of the Mithraeum | DATE/ERA: Roman, between the 2nd and 3rd century AD | SIZE: 29 m2 | LOCATION: Roman villa of Els Munts, Altafulla (Tarragonès) | CRBMC REGISTRY NO.: 10029 | COORDINATOR: Pere Rovira | RESTORATION: Àbac Conservació-Restauració, SL: Sílvia Llobet, Maria Molinas, Gemma Piqué, Jaime Salguero and Gemma Torra, and the interns from the CRBMC: Xavier Martínez, Marina Ramisa and Olga Schmid | YEAR OF THE RESTORATION: 2019 | CATALOGUING: Archaeological ensemble of Tàrraco declared a UNESCO Human Heritage Site. 2000. Cataloguing BCIN 2044-ZA