It’s unthinkable to imagine such a delicate operation, like the coverage of the ancient amphitheater, without reference to how the Romans of the time had faced and solved the question of coverage of the arenas, albeit for mere defense from sunlight, leading to define what is called synthetically “Velarium”.
In the Colosseum, the arena “par excellence”, as in many other contemporary amphitheatres scattered in Europe, the Romans had developed a “palliative” cover system which served to protect from sunlight the bleachers, and give some relief to authorities and spectators. Is nothing more that what today we might call the example of the proto-historic “tensile structure”.
The materials used for this coverage were basically three:
1) The wood for stakes that served as the primary structure,
2) The ropes in hemp and similar anchored to the wooden pillars, representing the tense structure, ending on boulders placed at street level,
3) Hemp textile anchored to cables, which served as a true and proper coverage, to shade the arena.
The wooden poles were properly anchored to the wall structure through slots, provided in blocks of stone, specially designed. The basis of the same rested on other segments shelf, in which “cup-shaved” concavity, the pole itself lay.
The ropes were pulled manually with the help of pulleys and put under tension the central “ring”, the radius of which varied as a function of the elliptical geometry of the arena. At the ropes were anchored with rings the hemp curtains (also double) upon which flowed to relax the tissue cut and sewn to size.
The references that have guided us, and that we followed to arrive at the present project conclusions, starting just from the “Velarium”, suggest us to highlight some differences and difficulties between the original Roman system and the project that we made for the Verona’s Arena.
Primarily, as we said, the Velarium was a very light and partial coverage (leaving exposed the central part of the arena) which was repaired from sunlight and wasn’t appropriate for rainy days. Given the consistency of the materials available at the time (especially hemp) the coverage was very unstable in presence of strong winds, who strained the warp of the plot of the same tissues up to the laceration of the sheets. In this case the Verona’s Arena coverage must be total, so, with the central part covered.
The following points summarize the hypothesized design solution:
>Historical reference: coverage of the entire arena in tune with the old solutions adopted at Romans’s time (Velarium) for similar and contemporary amphitheatres.
>Respect for pre-existing: full respect for the ancient monument with the introduction of external structural systems to the architectural shell, no invasive and completely detached from the walls of the Arena. The only point of physical contact, with the ancient masonry, consists in retainer anchoring at the top of the pillars, very important for the vertical static stabilization of the element. That anchor will be made in no inasive steel system and without piercing the wall of the amphitheater (no trace will remain before the disassembly of the structure).
>Minimal visual impact: sober and lightweight design which allows to minimaze the visual impact of the vertical structures in relation to the ancient artifacts and the group intervention in the neighborhood of the Arena.
>Assembly of the structure: assembly and disassembly of the roof structures (and related tarpaulins) in a simple and rational way, with the help of ordinary temporary works and machining times not long.
>Transportation and storage: lightness of the steel structures to facilitate transportability by ordinary means that can access to the old town without destabilizing the daily vehicular traffic and storage in normal-sized deposits.
>Inexistence of underground foundation works: The foundations of the pillars are essentially made up of stands placed directly on the ground without causing interference or damage to service infrastructure network lying beneath the road surface and without conflict with the archeological basement and foundations of the amphitheater.
>Openable cover: In close harmony with the Romans Velarium, the project expected that the cover with teflon sheeting is openable to a maximum of 80% of its extension. The sheets are therefore collected with electromechanical system and leaning towards the outer ring of the roof structure.
>Intervention’s cost: costs of realization of the entire structural system of coverage are very low, taking into account the extent of the great part to be covered (about 12.000 square meters).
>Economic maintenance: minimum cost of maintenance of the roofing system due to the use of stainless steels ad good quality of the covering sheets, also for long periods of permanence of the cover, in place.
>Easy contract and rental for the coverage: being the coverage realized entirely in workshop and then transported on site for assembly, seems possible to achieve the structure, contracting specialized companies, which then could rent them directly to the manager of the activities of the amphitheater exempting the Authority from heavy administrative and bureaucratic charges.
>Inexistence of the traditional building site: taking into account that the entire coverage has to be built in the workshop both for the mechanical parts (stands, pillars, trusses rings, cables, etc.) both for the teflon parts (sheets cutting and seam). It’s easy to imagine a “clean and dry” yard, achievable for parts, that will make minimum discomfort around the amphitheater.