Premise:
In 1997, commissioned by the Opera della Metropolitana di Siena, I began to develop a restoration project for a complex of spaces below, and partly adjacent to the Cathedral of Siena. They formed the original Oratory of St. John and St. Gennaro, more commonly known as St. John the Baptist.
The initial purpose was to restore and enhance the complex of St. John, which has been almost in disuse for many years, to include it in the museum tour of the Cathedral and the Baptistery. They develop an overall area of about 1000 square meters.
Works on site started with a series of preliminary surveys, which consisted of historical research; metric survey; trials into the walls, the horizontal structures, the foundation ground; stratigraphic investigations of ancient plaster and stucco.
Thanks to an infra-red micro-camera, we discovered the existence of another cavern, filled with rubble. Its emptying allowed us to find a tunnel, that from this cave, located at the level of the entry of St. John in Via dei Fusari, started climbing for about m. 7.50 towards of the Cathedral floor. This tunnel allowed us to make a discovery which proved to be stunning: a new room, which nobody knew existed - except for some vague references in a historical memory dated back to the beginning of the Sixteenth Century - and remained inaccessible because it was entirely filled with rubble.
This room, of an overall area of about 200 square meters and an average height m 4.50 ca., had been probably built in the late Twelfth / early Thirteenth Century , as a secondary entrance to the Cathedral. It contains a series of wall paintings which date back to the end of the Twelfth Century, and it’s of stunning value. The original purpose of this room fell into disuse when the extensions works to the Cathedral started, during the Fourteenth Century; then, in the early Fifteenth Century, with the construction of the Baptistery and the lowering of the presbytery floor, this space was permanently closed and used as a landfill for the materials from the construction site. And, amazingly, the remarkable and original marble floor of the chancel and the choir, which we still admire today, was built on this loose material, mostly coming from the demolition of the original vaulted ceiling (soil , pieces of stone and bricks, remnants of plaster and rubble waste in general) obviously constipated. The surveys led us to exclude the presence of architectural elements to support the floor, such as arches and vaults, on the entire area of the room!
Evolution of the project and the problems of museum use:
The importance of the discovery was such that it required to deal with new and unforeseen issues, as well as to review not only the original restoration project of the Oratory of St. John, but also time schedule of works and budget, which were non-trivial issues…
Once the first phase of study was completed, we had to decide what to do.
The issues to be addressed were briefly as follows:
- whether to undertake the difficult removal of the debris, more or less incoherent, which completely infilled the room we found;
- whether and how to consolidate and support the floor, excluding from the beginning the hypothesis of its temporary dismantling;
- how to reconcile, on the assumption of its complete emptying from the debris, the paramount needs of the consolidation of the floor and the conservation of the decorative paintings on the walls, with the possible opening of this space to the public as a part of a museum tour.
Eventually, after evaluating various hypothesis, it was decided to face the emptying of the room, starting from the cavity which had allowed its discovery, proceeding with a technique similar, so to speak, to a tunnel excavation. It was simultaneously developed a restoration project that included the musealization of this space, and its inclusion in a wider museum route covering all the spaces below the Cathedral, already described in the introduction.
The whole emptying procedure took about a year of work, in which approximately one thousand cubic meters of debris were removed. The constant presence on site of archaeologists allowed us to gain important documentary information about the construction history of the Cathedral, as well as to retrieve a large number of finds of various nature: fragments of frescoes, remnants of carved stone, coins, up to the simplest objects that document the life in a medieval construction site, but also many burials and even some mummified bodies.
The structure that would have bear the Cathedral floor after the emptying of the room would have had to simultaneously comply with two requirements:
one hand, it had to be easy to construct and / or assembly; on the other hand the maximum reduction of dimensions, to allow a complete and unitary perception of the room, particularly of the decorative set of wall paintings.
Also, there were other problems: the irregularity of the ceiling with steps and inclined surfaces, the irregularity of the perimeter walls of the room and the presence, within it, of masonry structures such as a pillar, two arches to support the pulpit, the bases of two pillars and two walls. Therefore the new structure should have had a remarkable ability to adapt and to be mounted through a modular system, while we were still keeping onsite the first structure, the provisional one: the new structure should have been able to replace the first one, without causing any trauma to the floor above, and indeed it should have had to allow it a slow adaptation to the new static situation, that was going to be modified after nearly seven centuries!
Since the interior space was, as I before described, already partially altered, there was the need to build a structure that did not compromise further the space, and particularly did not obstruct the reading of the various architectural elements and the decorations.
On the basis of all these considerations, I immediately opted for the use of a stainless steel frame, definitely excluding reinforced concrete, wood and any other technology.
The design started and moved towards the use of a modular structure, built with elements of small dimensions, easily assembled with bolted connections.
The structure we built is of a sort of grid made up of profiled flat bars, assembled on a cm60x60 modulus. A series of adjustable “feet” screws, adapt the grille to the ceiling surface which, as I explained, is not coplanar. The grid is in turn supported by eight rather slender cylindrical columns, whose stem ends with a sort of capital: from here, four inclined "arms" depart, to provide the connection between the grid and the column. The grid system was also designed to allow the housing of ducts and electrical and lighting equipments, and offer a great flexibility of use.
We mounted a floating floor made of wooden planks, mounted on a modular steel structure, restoring the original levels of the floor.
The metal structure, completely independent from the existing walls, has been designed so as to create a gap between the foundation level and the floor surface, to allow the passage of ducts for air conditioning and electrical systems, which remain hidden and are easily inspected. Finally, this solution is reversible, as it can be completely disassembled without creating alterations to the historic structure.