Cittadella di Alessandria 2

The buildings inside the Citadel of Alessandria: architectural and Construction History.

The research deals with the construction history of the buildings inside the Citadel of Alessandria. While these buildings are unquestionably part of our National heritage, they have never been considered, up to this day, in their complex materiality. The research aims to cross-reference the archival information on the citadel’s early history with the close observation of the buildings, in order to construct a plausible interpretation of their planning and construction process, and of their actual physical configuration. Among the research questions, at the time this report is going into print, are the following: what construction techniques and materials were employed in the Citadel? Who were the main actors involved and how do they relate to the state-of-the-art knowledge of their time? How did the buildings perform in their time? Were any crises and failures recorded, and if so, did they lead to improvements or modifications? How does the materiality of the buildings relate to the reuse / preservation / consolidation issues that arise today?

Year

2019

Research coordinators

Edoardo Piccoli, Cesare Tocci

Collaborators

Roberto Caterino, Elena Zanet, Temirlan Nurpeissov, Elena Rossi, Maria Chiara Strafella

Type

Project

Outline

The choice to focus on the 18th and early 19th c. large-scale buildings of the Citadel in Alessandria, rather than on the better-known infrastructural and defensive works, has allowed us to venture into the somewhat uncharted territory of the buildings’ planning and the detailed choices leading to their construction.
The information assembled will allow a more competent examination of structural and planning issues in future interventions, and provides also a guideline for research/reuse / preservation issues both in Alessandria, and in similar sites elsewhere.

In the first phase we followed two main lines of investigation:

  1. The in-depth archival reconnaissance, within the Buildings’ and Fortification Agency funds (1730s-1800) in the State Archives in Turin, with secondary investigations in Rome, Paris, and in other Turin archives. The more than 400 contracts retrieved, along with the countless other items, from royal Decrees, to expense charts, to copy-letters, instructions, drawings and judicial funds, have allowed us to track and summarize in detail the 18th century evolution of the construction site, drawing a map of the authors involved, as well as of the materials, and technologies (a similar detailed knowledge of the ‘French period’, i.e. 1800-1815, remains a more open question, due to the loss of most archival funds).
  2. The thorough inspection of the accessible parts of the site, through several site visits, leading to a first-hand knowledge of its layout and constructional characters; the inspection was followed by a closer observation, with partial surveys – dramatically, no general survey of the site is yet available, as we write -, of three of the 18th c. buildings: the S. Tommaso and S. Carlo barracks, and the military Hospital.

Following this first phase, which led on the one hand to a quite massive collection of digitized and transcribed archival documents, and on the other, to a collection of documentary evidence on the buildings (photographs, drawings, partial measurements), the group has worked together in the examination of a selected number of problems, which we felt were particularly urgent, historically relevant, and useful for the citadel’s future conservation. This part of the research is still ongoing, and we can summarize it in the following points.

Masonry construction

The buildings within the citadel are a remarkable example of brick masonry construction. Almost 100% of structures are made of brick masonry (tens of millions of bricks, produced on or near the site; different kinds of mortar; limited use of wood, iron ties; almost no natural stone), with very small but significant variations in units arrangement and bonding types as well as peculiar constructional details, over the first century of construction of the military complex.
The Citadel’s buildings are obviously comparable with classical masonry work but their enormous dimensions introduce significant variations that are worth of specific examination: the role of mortar can no longer be overlooked, as against ordinary buildings;
the mutual elements’ connections, that the wall thickness makes far more effective than usual, are also relevant; the plan configuration, finally, is not so strictly related to horizontal slenderness of perimeter walls, as in normal constructions.
While these buildings look simple, almost every choice or detail is the result of careful planning, given the quantities of materials and workmanship involved: therefore, even the understanding of a few basic facts about their constitution required accurate research and cross-referencing. After establishing a consistent timeline of construction and recovering a few key documents (general and specific instructions for building, drawings, etc) we were able to debunk a few ‘myths’, such as one regarding the piecemeal reuse of materials from the demolition of the city buildings (which proved false, as the reuse of old materials was in itself a carefully planned operation). We then could move on to more detailed analyses (points 2,3).

Foundation systems

The terrain on which the citadel stands is not suited to heavy buildings: the soil in the area is soft, the water table high, and flooding from the river frequent: indeed, water is still, in Alessandria, a constant menace, and the last devastating flood has taken place less than thirty years ago. For this reason, wooden pile foundations have been used throughout the site since construction started, in the early 1730s. The research has uncovered the procedures and materials used for foundation systems, and has established that due to an early (1750) episode of structural failure in the S. Tommaso barracks, a heated debate developed, leading to the adoption of an improved system in the later 18th c. buildings. Accurate drawings have been produced by the research unit, representing the two foundation systems detailed in the construction specifications. The information and interpretation of this data allows to approach conservation issues in the damaged barrack (where cracks and fissures are still apparent), and will be a guide in further research and analyses of the structures in all buildings.

Bomb-proof vaulting and massive roof structures

The constructions within the citadel built before 1815 were made to be bomb-resistant, or bomb-proof (à l’épreuve). 18th century construction practices defined different ways to achieve this result, the most common ones being:

  1. The use of “normal” – or slightly stronger than ordinary, through the use of thicker top-level vaults– buildings, coupled with wooden roofs that could be dismantled in the event of a siege, thus leaving an open terrace that would then be protected by a layer of compressed earth and rubble, while temporarily propping up the vaults and buttressing the external walls to support the increased weight and thrusts.
  2. Massive constructions with astonishingly thick walls and top vaults – the latter topped with layers of compact masonry (massiccio), forming the slope of the roofs, and directly supporting roof tiles – that could withstand bombs’ impact without being pierced nor losing equilibrium. Such technology seems to have been developed in the 17th century especially for powder magazines.

Both solutions are used in Alessandria, in one instance combined in the same building (the Hospital), with a prevalence of the second method: in fact, the Citadel’s buildings constitute one of the most consistent and extensive existing examples of ‘type b’ bomb proof construction. Our research has determined the specifications, debates, and evolution in the use of this technique, in connection with the general planning of the buildings, the design of the vaults, the use of hidden iron and wooden ties, and of ventilation tunnels. The major problems that have recently arisen at the Citadel in roof maintenance and waterproofing make this part of our research a necessary step towards a rehabilitation of the citadel’s inner works.

Conclusions

Construction history, in our view, is not just an ancillary knowledge to restoration. As related to social, economic history and to history of science, it is an indispensable research method when approaching a compound such as the citadel, where design and construction developed, in the period recorded, combining different areas of professional knowledge and of production: structural engineering, civil and military architecture, infrastructure planning, landscaping, ballistics…
While we have barely opened up certain topics for further analysis, our research has improved existing knowledge and provided new insight in the following areas:

  • the buildings’ construction history, from their origins to their present state;
  • the buildings’ typological characters, and their transformation potential;
  • the definition of guidelines for future surveys, structural analysis and tests on materials, highlighting the urgent need for a detailed geometric survey and selected tests;
  • the valorisation of the Citadel’s architectural heritage, with new narratives and details on construction that may be made available to the general public;

The research, finally, suggests that it would be necessary to pursue further historical investigation, especially on the construction history of the outer works and of the 19th and 20th century structures.
Parts of this research have been discussed in conferences in Turin (FORTMED International congress, oct. 2018), Cambridge (Construction History Society, april 2019), Venice (IUAV / Société de Histoire de la Construction, International seminar on Expertise in architecture in the XVII-XVIII c.). Other research seminars have involved the staff of FULL and colleagues from the CAST research group on the citadel.