The first “Conservation Plan for the Monument” (Preliminary project report and definitive project), developed from an idea by A. Vodret, was drawn up by the Soprintendenza Speciale per i Beni Archeologici di Roma in March 2011 and written by F. Filippi, A. Vodret, I. Sciortino, E. Segala and M. Pesce. It was then presented to the Technical Committees for Archaeological, Architectural and Landscape Heritage of the Italian Ministry for Cultural Heritage and Activities (MiBAC). Subsequently, those parts of the project concerning the consolidation of structures and decorations, and the tests for the proposed new arrangement of the waterproof roof were launched.
The Domus Aurea
Few places of classical antiquity contain within themselves such profound meaning as the Domus Aurea for the history of Italian artistic culture, especially that of the Renaissance. The way in which the pavilion on the Oppian hill was rediscovered contributed in no small way to creating that evocative fascination that still today surrounds its visitors and that originates from its discovery.
When, towards the end of the 15th century, numerous visitors began to lower themselves into the underground grottoes and discovered the painted vaults by torchlight, they copied and disseminated the decorative motifs, in a crescendo of interest on the part even of important artists working in Rome at the time.
We can only allude briefly here to the truly fundamental influence exerted on Renaissance art by these paintings in Nero’s palace, attributed by the sources to Fabullus, but it helps us to understand the unique importance of the Domus Aurea archaeological complex for modern culture. This forces us to reflect carefully on the need for constant commitment to its difficult conservation.
These are factors that determine both the importance and the appeal of a monument whose exceptional size reflects the magnificence of the imperial palace: a floor area of 16,000 square metres, 30,000 square metres of frescoed surfaces, a height of up to 11 metres at the underside of the vaults within its 150 rooms.
This sense of grandeur is further heightened by the palace’s current underground state, which makes a great impression on visitors. It should be remembered that the pavilion built on the Oppian Hill, with a façade length of 240 metres and a width of between 30 and 60 metres, was just a part of a more elaborate terraced complex, with a lighter upper storey set in vast luxuriant gardens. It overlooked the valley with the great lake (almost a sea) where the Colosseum was later built, a building for spectacles that became a symbol of the return to the people of Rome of the urban land appropriated by Nero.
35 years after its construction, in AD 104, the Oppian Hill and with it the pavilion of the Domus Aurea, partially destroyed by a fire, was occupied by the grandiose Baths of Trajan. The upper storey was destroyed, the rooms on the lower storey stripped of their marbles and valuable materials and partly occupied by the imposing substructures of the baths, the “Trajanic Galleries”. Today, these lie inside the archaeological complex and form its façade towards the valley, albeit with a different orientation from the earlier building. Nero’s pavilion was buried and became a vast platform on which the new baths were built; their remains form the archaeological landscape of the Oppian Hill today.
The constituent parts of the monument as it has been preserved for us by history in all its transformations ensure its cultural importance and enhance its appeal. However, they also create very specific and extremely complex conservation problems: we are dealing with a delicate and precarious architectural complex, an underground monument overlain by a park consisting of a 2-3 metre thick layer of earth weighing on its vaults and hosting trees whose roots penetrate into the ancient brickwork; the relationship between different construction phases – Neronian and Trajanic – further complicates these conservation problems whilst the unusually large size of the complex multiplies them and sometimes makes it impossible to achieve any of our objectives.
Together these features cause the decay of the structures and the painted heritage of the Domus and must be constantly controlled, especially as concerns the fundamental issue of the climatic/environmental and microbiological equilibrium. Any plan for intervention, even a partial one, must be evaluated with all these issues in mind and in the context of the constant relationship between interior and exterior: recordings have shown that merely erecting scaffolding leads to changes in airflows and thermo-hygrometric levels, with immediate repercussions for the conservation of paintings. Equally, the instrumental monitoring of structures, connected to alarm systems, is underway inside the monument where there are significant cracks that might compromise its stability.
One of the main causes of the decay of structures and paintings is the constant exchange of air with the outside and the extremely high levels of relative humidity, due mainly to the fact that the complex is currently underground. Evaporation/condensation on the surfaces leads to the crystallization and solubilization of salts, but also to the solubilization and crystallization of the calcium carbonate in the mortars. This causes two forms of decay: whitish efflorescences and decay of the mortars, belonging to both structures and painted surfaces.
The presence of air inside also contributes to the risk of diffusion of chemical and biological contaminants (bacteria and fungi) which may attack the structures and colour them black and green, with consequent damage to stucco elements and paintings. Anyone entering may also bring biological contaminants with them.
Instrumental monitoring of the microclimate, in relation to external climate conditions, has been underway for some years in the Domus Aurea. The optimal reference values for the conservation of wall paintings, frescoes and underpaintings (temperature between 10 and 24 °C and relative humidity of 55/56%) are obviously not applicable to underground wall paintings, saturated with damp: the humidity of the surrounding air must be such as to avoid any evaporation from the walls, as this is a destructive process. University specialists and experts who collaborate with the Management of the Domus Aurea on an ongoing basis agree that stabilizing the temperature and relative humidity are essential for its conservation; it is also clear that there must be no percolations of water from outside. The climatic microhistory of the monument tells us that during the summer the air temperature inside is about 16-20 °C with 85/97% humidity, whilst in the winter the temperature is 9.5/11.5 °C with a relative humidity of 80/90 %. The values considered favourable are a temperature of 17°C +_ 2, a relative air humidity of 92.5%, an air speed of < 0.4 m/s and light of under 150lx.
How can we create genuine and lasting conditions of stability when there is a park above the underground monument, consisting of an extremely thick layer of earth that absorbs and transmits to the interior any change in climate, like rainwater from a storm?
It should be said that the conditions are, as always in such cases, extremely complex: this same layer of soil paradoxically “protects” the stability of the internal climate, for example from the torrid summer heat which would, in direct contact with the structures, lead to the desiccation and detachment of the painted decorations that, as we have seen, are preserved in a very humid environment. Similarly, the desiccation of the roots of a tree would lead water to percolate inside onto the paintings through the empty space created. Attempts made over time to waterproof the layer between the park and the ancient structures have not provided the hoped-for results, given the complexities of maintaining the waterproof layer, the difficulty of keeping drainage levels in equilibrium over time in the presence of easily compressed made-up ground and the fact that these are in any case partial interventions which, even were they to succeed in covering the entire surface of the monument, could not prevent water running off its edges.
The archaeologists, architects, engineers, conservators, physicists, chemists, biologists and botanists who have been studying and working inside the Domus Aurea for many years all agree that to successfully reduce climate instability, the principal cause of risk to the monument’s conservation, beyond the plan to secure and consolidate the structures and painting cycles, we need to tackle holistically three aspects which the Soprintendenza has adopted as the fundamental parameters for its own General Intervention Plan.
The first is to implement a process of isolation of the internal spaces from the outside, both by progressively closing apertures in the structures and reconstructing missing vaults, and by compartmentalizing the rooms with painted decorations so as to significantly reduce the air flows that fluid dynamic studies by CISTeC have shown to have a marked impact on the stability of surfaces. This programme must be complemented by developing visitor routes, again demonstrating the unbreakable bond between safeguard and enhancement and, eventually, open access to heritage.
The second concerns the overall consolidation of the monument, already underway inside. To achieve this, close coordination with interventions from outside is necessary. A programme of archaeological research has begun. The outside of the vaults present a variety of situations: incoherent materials but also floors and walls belonging to the first storey of Nero’s Domus (East Wing), or the structure of Trajan’s baths (for their whole extent). It is obvious that we cannot simply consolidate the whole depth of the stratigraphy.
In this extraordinary situation created by an extraordinary monumental complex, the project must systematically tackle the situation above ground, now the Oppian Hill park. It would be impossible to proceed in accordance with the classic methodology: the preventive and extensive excavation of the stratigraphy – which, as we have explained, would cause a shock with dramatic consequences – with the aim of drawing up a project to conserve and waterproof the outer surfaces of the monument. This forces us to make a different choice, aimed at the gradual and constant completion of the overall consolidation of the ancient outer structures, currently preserved under the earth of the park.
The most delicate aspect of the project concerns the on-site phases (excavation – consolidation – waterproofing – new park), which must be carried out without interruption.
This process, covering the whole monument, also forces us to make a more general decision regarding the fate of the Domus Aurea’s environmental context. The damage caused by the collapse of the park above a Trajanic Gallery (30 March 2010) is no longer acceptable. We need an evaluation that comprises the landscape and topographical features of the urban context of the Oppian Hill: the area’s principal vocation as an archaeological site, already apparent from the imposing remains of Trajan’s Baths, must also ensure the survival of the underground monument.
We are currently testing a system to protect the ancient structures and reorganize the park area above the Domus Aurea with a lesser depth of soil, as part of a project to enhance the perception of the terrace of Trajan’s Baths and recompose the stratigraphic and historical relationship between these two large monumental complexes. The results of the test, whose second phase is currently being concluded, will shortly be completed with data analysis.
We will provide news of the results. The project considers the Domus Aurea an integral part of the Oppian Hill park and aims to recreate the stratigraphic, structural, architectural and topographical relationship between the underground Neronian pavilion and the terrace of Trajan’s Baths. The different orientation and the substructures of the latter have fundamentally altered the visual perception of this relationship and we therefore need to recreate their planovolumetric links within the current landscape of the Oppian Hill.
In our view, the failure of the various projects hitherto developed can be explained by their approach to conservation problems. Even in the case of the Domus Aurea, technological choices must necessarily follow, and not precede, knowledge.
We have therefore tried to reverse the order of progress and at the same time identify two approaches that underlie our project guidelines:
- the first is to formulate a potential layout for the Oppian archaeological area around the Domus Aurea, to be confirmed or modified by archaeological data, strictly governed by a correct architectural recomposition;
- the second is to define a “code of conduct” for technical solutions to protect the monument against percolations of rainwater and variations in the microclimate, not in an indiscriminate way but as a function of the typology of the architectural structure and its state of conservation.
The Domus Aurea came into “architectural conflict” when the Baths of Trajan were built; the former, originally an overground building on a terrace, became an underground foundation on which to construct the latter. Today’s challenge is to find the point of integration between archaeology and conservation in the attempt to eliminate this conflict, establishing a dialogue between the two architectural complexes, whilst still respecting their different meanings. We must accept the evident fact that history has passed down to us a complex profoundly altered in its original topographical, structural and architectural nature, which we need to respect today in its final layout.
The general principles that we have adopted therefore reflect the need for conservation, but also the need to rehabilitate a complex archaeological area, to be read through its historical stratigraphy, and to be inserted in a new and coherent way into the archaeological landscape of the Oppian Hill.
The project idea
The aim of the project is to conserve the Domus Aurea in its peculiarity as an underground monument, through an integrated intervention – philological, archaeological and functional – that includes recovering the complex “above and below” and rehabilitating the terrace of Trajan’s Baths within the context of the park. We intend to gradually create a new landscape that enhances the visual and physical perception of the ancient monuments, recreating the planovolumetric relationships between them and thus ensuring their spatial and cultural reconnection with the Colosseum Valley and the Central Area of the Palatine and the Imperial Forums.
The underground complex of the Neronian Domus lies immediately beneath the southern perimeter of the central block of Trajan’s Baths, with a different orientation. This was a vast terrace on substructures, with monumental exhedras (nos 2, 3, 4) at the edges. The external perimeter, as excavations have demonstrated, was defined by a colonnaded portico facing onto an open area, already used as a garden (xistus) in antiquity.
Our idea is to design the park, at least in the southern area, above a new layer of earth less deep than that of the current park. We will recreate the basic layout of the ancient portico and large southern exhedra to create at least a visual link with the other exhedras (nos 2, 5, 7) and make the “Terrace of the Baths” once again a place to stroll, play sports, enjoy leisure, culture and competition in accordance with their ancient function.
Although more detailed information will be supplied by archaeological excavations, at the current state to advance in the development of our project we can make reference to what has already been ascertained: the known data are extremely detailed and inhomogeneous in the various areas. However, we already know that the project must tackle three different levels of ancient structural remains, not all of which were contemporaneously preserved or present.
Beneath the layer of earth of the park, excavations may identify:
- remains of post-Trajanic phases (Severan interventions on the Baths; buildings of the 16th-18th century)
- remains of the Baths of Trajan: two types of floors (opus spicatum, bipedales over a cavity with little pillars of bessales) at different heights; underfloors in opus coementicium; the outer surfaces of the vaults of the substruction galleries at different heights;
- remains of the Neronian Domus Aurea: structures of the upper storey; outer surfaces of the vaults of the lower storey;
Q: What is the idea underlying the project?
A: To use these archaeological remains, currently covered by the earth of the modern park, and to conserve and repair them using their constituent materials to protect the rooms underneath. This will allow us to achieve the objective of rehabilitating the ancient architecture of the Oppian Hill, recreating the juxtaposition between Trajan’s Baths and the Domus Aurea and thus resolving the current conflict.
Q: How will we deal with the ancient structures identified by excavations?
A: We will use them, conserving them and repairing them as one of the protections for the underlying structures: this is “conservative improvement” work. All this will not, however, be sufficient to protect the decorative heritage underneath: we will need a protective layer that is much less thick than that of the present park, hosting the waterproofing and thermal insulation layers. The tests underway suggest that the new layer (waterproofing layer and new park) will be no more than 1 metre thick.
Given the failure of waterproofing systems in direct contact with the outer surfaces of the vaults or in the earth layer, the project solution is to intercept water on the surface or at any rate at the highest possible level to facilitate its removal and maintenance of the drainage system.
Q: What is your code of conduct?
A: To consolidate and repair the ancient structures above the Domus using traditional materials. To create, above the ancient remains conserved, a “sacrificial” technological package consisting of materials with a high thermal inertia coefficient that do not hinder transpiration and that ensure the interception of rainwater at the highest possible level. The system has been subjected to physical simulation tests (1st test phase); currently it has been placed directly on the outer surface of a Neronian vault and we are testing its behaviour by recording the variation in the parameters of seasonal hygro-thermal variation (2nd test phase). The results will be available in the autumn of 2012.