Multidisciplinary approaches for the study and reconstruction of the Roman theatre of Nora (Sardinia, Italy)
The main aim of this thesis, by the author Héloïse Rostagni is to recover the original aspect of the Roman theatre of Nora in Sardinia.
CITY OF NORA
Nora is one of the most important archaeological sites in Sardinia.
The town is located at the tip of Capo Pula, where it has always served as a decisive port for trade throughout the Mediterranean.
As shown in Fig. 4 and Fig. 5, the ruins of Nora are an open-air museum, and the remains of the theatre are sometimes used for concerts and performances in the summer.
Founded by the Phoenicians between the 9th and 8th centuries BC, its stratification from the Phoenician-Punic period is now covered by the ruins dating back to the Roman domination, when, conquered in 238 BC, it was elected municipium and enjoyed its greatest splendor.
Fig. 12 – Principal events in the history of Nora.
HISTORICAL BACKGROUND: ROMAN THEATRES
The word “theatre” is derived from the Latin word theatrum, which in turn comes from the Greek theatron (θέατρον) and means a place to see [performances].
Roman theatres were thus complex buildings, closer in their design to modern theatres than to Greek theatres; although their architecture is mainly based on that of their Greek counterpart.
The first examples, the theatre of Pompey and the theatre of Marcellus in Rome (see Fig. 21), establish a new form, different from the open Greek model: the Roman theatre is a closed monument in which the tier of semicircular tiers joins a luxuriously decorated scene building. The construction technique, the use of walls and radiating arches to support the tiers, allows building on flat ground and exempts from leaning on a hill as in the Greek style.
Differences between Greek and Roman theatres
Differences can be noted between the ancient Greek and Roman theatres such as:
- The most obvious one concerns the landscape typology chosen for the structure. Greek theatres were built in the landscape, whether on hills or other naturally sloping faces. This allowed greater ease of construction (at lower costs) and brought natural stability to the structure, especially to the seating area. Roman theatres, on the other hand, were generally built on flat, properly stabilized ground
- In contrast to the Greek model, they were closed buildings: while Greek theatres offered spectators a view of the surrounding landscape behind the scene, a scene wall closed Roman theatres and rose to the same height as the cavea.
- This leads to differences in the organization of space (see Fig. 23). Indeed, the seats were arranged in a semicircle around the orchestra in the Roman theatre. But the scene and scene building were connected to the auditorium and rose to the same height, creating a feeling of enclosure closer to that of a modern theatre.
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ROMAN THEATRE ARCHITECTURE
Roman theatres consist mainly of three parts:
- The stage of the Roman theatre was exceptionally wide and deep and was closed on three sides by high walls.
- The orchestra of the Roman theatre is built more or less semicircular. It is no longer used for performances: the spectators simply sit there, separated from the other spectators by a thin wall of stone or marble (balteus wall). It is then partially occupied by movable seats (bisellia).
The cavea was the place where the public was seated. With its tiers of concentric semicircles, it can be geometrically represented as a truncated cone cut vertically in half. The cavea was divided into different zones to organize the stratification of the audience that came to the performances according to their social rank.
Fig. 24 – Roman theatre nomenclature. [Data from THEATRA]
BUILDING MATERIALS AND TECHNIQUES
Roman builders used natural materials, mainly stone, wood, and marble; manufactured materials such as brick (dried or fired); and composite materials such as concrete. The choice was made on the basis of the availability of materials near the city, their physical and mechanical properties, and the type of elements to be built.
The most common and most logically used building material in Roman construction, particularly theatres, was still stone. Roman builders used several varieties of stone, each of which was valuable for certain qualities:
Examples of construction techniques
The Romans based their constructions on plans drawn up by architects. Once the plans were drawn up and the site chosen, excavation work was often necessary.
The Romans did not necessarily demolish and remove all buildings on the site. Often the earlier foundations were encased or vaulted over, or an older building was filled with rubble and built into the foundations. Sometimes, when it was necessary to lower the ground level, excavations were conducted.
A whole procedure was followed for erecting the walls. Scaffolding was used: holes were made in the wall to allow them to be connected to the structure.
DESIGN OF THE ROMAN THEATRE
The theatre of Nora is, to this day, the only known Roman theatre in the whole of Sardinia. The construction of the theatre was an episode of fundamental importance in the work of monumentalization of the center of Nora, undertaken with the construction of the Forum, the Temple, and other associated buildings.
In substance, with the construction of the theatre, the municipality of Nora acquired a building characterized by a strong political and ideological value, in accordance with the new legal-administrative status of the city, which was confirmed by the location of the structure near the Forum. The topography of the city, however, conditioned both the location of the theatre and its orientation.
The theatre of Nora was built according to the classical plan of ancient Roman theatres, with its semicircular configuration articulated in cavea, orchestra, scene building and portico. The distribution scheme is normal in its functional layout, close to that dictated by Vitruvius, but nevertheless had some particular characteristics:
The original structure of the theatre thus dates back to the first phase of construction. Some theater features:
- The outer curvilinear elevation of the cavea, originally divided into two levels by a moulded frame, appears to be divided by eleven compartments.
- The cavea, designed to accommodate spectators, was about 39 metres in diameter and was of medium to small size.
- The first sector of the cavea was therefore made up of eleven rows of semicircular steps with a minimum radius of curvature on the orchestra floor of 6.80 metres and a radius at the top of 13.40 metres.
- The profile of the cavea was inclined at 38 degrees to the plane of the orchestra, allowing a tread of 0.60 metres for the steps with seats and a rise of 0.46 metres.
- In total, the capacity of the theatre had to be about 1100 to 1200 seats, which is almost double the capacity calculated in the past on the basis of the remaining steps alone.
- The orchestra was then accessible from outside through two vaulted passages, restored in the twentieth century.
- The semicircular orchestra is 13.40 metres in diameter.
- The orchestra was bounded by the cavea and the stage wall.
- As was usual during the Roman Empire, the walls of the cavea were connected directly to those of the scene building.
- The scene building closed off the semicircle of the theatre formed by the cavea and the orchestra at the side of the Forum.
- The whole scene building consisted mainly of the proscenium, the hyposcenium and the scaenae frons.
- The scenic area was flanked by two 20 square metre rooms (parascaenia)
- Opposite the cavea was the scene back wall.
- The theatre of Nora have modest porticus post scaenam, composed of a single colonnade.
- It was possible to enter the theatre in three ways: from the top of the cavea, directly into the orchestra and via small doors that opened from the portico behind the stage.
- Information about the water flow indicates that the theatre did not have a roof. The water that rained in the cavea was channelled to the orchestra. From there it flowed into a drainage channel that crossed the stage in the centre, continuing under the portico and the road until it reached the Forum and then into the sea.
BUILDING MATERIALS, CONSTRUCTION TECHNIQUES
Regarding the construction techniques and materials used, the theatre of Nora seems to be made entirely of large square blocks of different kinds of stone (see Fig. 45): volcanic rocks mainly dacites for the steps of the cavea, sandstones and conglomerates in the outer masonry and the scene.
In addition, there is evidence of the moderate use of concrete (opus caementicium) and the use of bricks in the fillings of the substructural niches of the cavea (see Fig. 48) and in the murus pulpiti.
Most of the theatre is built with Tyrrhenian beach sandstones and conglomerates; they occupy the outer hemicycle, the scene and the porticus post scaenam. They have been used not only for the structure, but also for some decorations of the outer hemicycle. Some blocks are made entirely of sandstone, others of conglomerates, and some show the transition from conglomerates to sandstone.
The aim was to create a three-dimensional visual model of the structure in its original state, i.e. with the missing parts and without damage. In order to provide a model as faithful as possible to reality, this model is based on the archaeological information collected, as well as on the geometrical sounding carried out on site and provided in the form of AutoCAD plan and sections.
The 3D reconstruction was carried out using AutoCAD 3D software. The different parts of the theatre were drawn: the cavea, the orchestra, the scenic building and the porticus post scaenam. The dimensions and shapes were respected with regard to the existing parts, those of the missing parts had to be approximated from the known data on the Nora theatre as well as on Roman theatres in general.
The purpose of this model, in addition to showing the monument in its original state, is to fully understand the structure in its original state, as well as the construction techniques that may have been used in the not preserved parts of it.
All the data collected was evaluated and used as appropriately as possible for the final reconstruction.
Not all the data collected belong to the target period (due to the fact that the Nora theatre underwent several phases of construction), and not all the data necessary for the construction of such a model are available today (or no longer). Therefore, a sorting was carried out in order to select the data corresponding to the study period, which corresponds to the end of the third phase of the theatre’s construction. These data were then supplemented with appropriate assumptions.
The main input data that could be used for this thesis are photographs taken during the archaeological excavations, written documents describing the building as a whole, the materials, and construction techniques, based on the excavations, writings, and photographs describing Roman theatres, and the plan provided in Fig. 52 (corresponds to the ruins of Nora’s theatre in its present state).
Due to the small size of the theatre, the reconstruction of the destroyed parts was supported by images of Roman theatres of similar size. The website presenting the archaeological site of Nora also offered a 3D reconstruction of the theatre. Some modelling ideas are based on this reconstruction, but with a critical eye, using the archaeological and geometrical data collected.
Summary of key data
Several hypotheses were taken to carry out this 3D reconstruction. These hypotheses mainly concern the degree of precision of the drawn geometry, as well as the design of the partially or entirely destroyed elements.
The 3D virtual model of the theatre of Nora was made accurate to within 2% for the existing parts.
Another assumption that was made concerns the height of the ground around and under the theatre.
The studies carried out, and the data collected during the information-gathering phase did not allow a sufficiently high level of detail to be obtained for the entire building. For the sake of proper interpretation of the model, these architectural details were not drawn. As these details do not provide important elements in terms of understanding the building, it was chosen not to represent them.
Fig. 56 summarizes in pictures which areas are preserved or have been destroyed.
ISSUES AND SELECTED SOLUTIONS
The desire to achieve a complete and accurate 3D reconstruction raised many questions. Solutions have been implemented for:
- Porticus in summa cavea
- Praecinctio and vomitória
- Aditus maximus and tribunalia
- Scenic building
- Porticus post scaenam
This 3D reconstruction model of the final product is an adaptation of the third 3D reconstruction following the choices made at the conclusion of the structural analyses. Indeed, these analyses supported the choice of solutions by validating the design of the roof and all the layouts of the frons scaenae.
- For the roof, the secondary beams were modified (the section of 100 x 100 mm became 100 x 150 mm, their spacing remained the same); the primary beams were modified (the section of 100 x 200 mm became 250 x 400 mm, their spacing was reduced to 2 metres, i.e. about three times less).
- For the frons scaenae, a tapered wall is considered (which allows to respect the non-straight configuration of the scenic building, due to the presence of a road near the porticus post scaenam). Then, the maximum thickness was chosen but using the three-leafes wall construction technique: the façades are sandstone ashlar cladding, while the core is an opus caementicium (Roman concrete). In addition, it is added that the foundations of this back-scene wall are considered entirely of stone blocks in order to respect the archaeological assumptions.
In order to make the 3D model more realistic, a rendering can be performed. Two examples of possible renders are given below.
- The first way of rendering is simple and consists of placing the 3D model in a neutral and uncluttered environment. A white color was chosen to avoid giving a mock-up side to the 3D model. A use of 3D printing type to make figurines of the theatre of Nora would be interesting.
- The second way of rendering is more elaborate; it consists rather of a 3D visualization model that allows you to see the building evolve in its real environment. However, the materials used for the second rendering do not correspond to Nora’s (at the level of the orchestra, and the masonry used is not the right one). The use of orthophotos could, for example, improve this representation by applying the actual documented characteristics of the materials.
Fig. 111 – Rendering for 3D visualisation.
The study of theatre of Nora raised many questions that had to be resolved using the data that was available: written documents, photographs, simplified plan, and sections produced following a terrestrial laser scan. For the areas that were destroyed, this required more time and discussions with experts.
Comparisons with existing Roman theatres were carried out. This led to the definition of, for example, a probable design for the roof of the stage building, as well as for the frons scaenae. In order to validate or not the assumptions taken, it was decided to carry out a verification of the roof elements based on a simplified Eurocode calculation and a parametric analysis of the frons scaenae in order to determine its geometry (shape and dimensions) as well as the construction technique (and associated materials) used.
After having confronted the different hypotheses with archaeological considerations (notably concerning the choice of construction techniques), they were confronted with engineering considerations (particularly concerning the mechanical properties of the materials or structural stability problems). The analyses were carried out successfully.
- The result was that the configuration chosen for the roof was acceptable and stable with regard to the possible loads applied to it.
- With regard to the frons scaenae, the results of the parametric analysis showed that different configurations for the wall were possible. The tensile and compressive stresses are well contained between the strength values of the materials considered for the two types of construction methods. The analysis therefore made possible to validate the archaeological assumptions made. A review with the archaeologists has been initiated and led to the decision that the wall would be considered tapered in order to best match the laser scanning survey. Regarding its dimensions, they were chosen as the widest (2.16 m / 1.74 m) because a stone from the foundation of the wall is still present, and its size is of this order of magnitude.
- For the construction technique, a compromise was made. Indeed, the foundation stone is large and wide, which implies that the foundations of the wall were necessarily made only with sandstone blocks in masonry. However, due to its large thickness, it did not seem consistent to keep this technique over the entire height of the wall (heavy wall, and large amount of ashlar to be used). From these considerations, it was chosen that the wall was built as an opus caementicium with a sandstone masonry lining.
- Thus, these two structural analyses made it possible to take some modelling decisions and respond to the open issues related to the scenic building.
Through the work carried out for this thesis, the question of the importance of the cultural heritage conservation was addressed. Indeed, through all the information collected, the importance of preserving all the knowledge acquired in the past was noted, as it allows us to:
- Understand how structures work;
- Understand why a particular material or construction technique was used.
For the cavea, there is still an unsolved issue linked to the support of the tiers. The fact that the type of construction for the theatre is mixed (artificial embankment for the ima cavea, sub-structural niches for the summa cavea) is well documented. However, it would be interesting to study this part in order to better understand how the steps behave, how much material was used, how far from the surface the embankment is located, etc.). Indeed, during the 3D reconstruction, there are areas under the seats that remain poorly defined. Future work could provide answers and complete/improve the virtual model produced.
Analyses can also be carried out on these 3D models in order to run different scenarios (e.g. seismic, wind, flood studies).