The Cover for the Tombs of Postumio and Tres Puertas proposed by Nd_Arquitectos is an all-encompassing synclastic mesh cover that unifies both sites. The piece rises like an artificial topography that minimises the impact of its supports to blend into the landscape of the necropolis. The intervention improves accessibility through a system of reversible walkways that facilitate transit and act as hidden supports for the ventilation system.
Technically, the cover is resolved by means of a mesh of arches with variable curvature and a double PVC textile envelope with an intermediate air chamber. The system integrates an active protection network with sensors and extractors that automate air renewal to reduce CO2. The industrialised, minimal-footprint assembly is recyclable and reversible, using bolted joints, CHS tubular profiles and steel ballast boxes that avoid invasive foundations.
Cover for the Tombs of Postumio and Tres Puertas by Nd_Arquitectos. Photograph by Jesús Granada.
Project description by Nd_Arquitectos
And the temple became a sustainable machine…
The project has been carried out with funding from an Excellence Project grant under the Andalusian Plan for Research, Development and Innovation, 2021 call, supported by the Regional Government of Andalusia, Ministry of University, Research and Innovation, General Secretariat for Research and Innovation. It has also benefited from the invaluable collaboration of the Archaeological Complex of Carmona (Seville).
Currently, the Necropolis of Carmona is configured as an enclosed site where nature and archaeological remains coexist, organized around a pedestrian pathway that structures the visitors’ route. Most of the tombs, of very diverse sizes and originally excavated into the natural rock, are open, without covers, along the edges of the different paths.
The two adjacent tombs subject to intervention (1st century AD) present very different configurations. The Tomb of Postumio consists of a large sunken courtyard excavated into the rock about 5.00 m deep, measuring 7.00 × 7.70 m², which gives access to a single chamber with an approximate volume of 7.77 m³, containing niches for urns and a burial space for inhumation. It is a visitable tomb with restoration interventions carried out in 2019. The Tomb of Tres Puertas is a hypogeum-type, collective tomb composed of three chambers equipped with niches for cinerary urns, with volumes close to 3.00 m³ each, and a common access shaft. It lacks sufficient accessibility conditions for public dissemination, even though it shares an access path with the Tomb of Postumio. The right-hand chamber shows stability issues in the vault, as well as a direct connection through an opening in the rock to the courtyard space of the Tomb of Postumio.
The tombs would go unnoticed in the landscape were it not for the topographic variation that rises at their location, forming a slight mound surrounded by trees of varying sizes.
Due to their current geometric configuration and the nature of the terrain (poorly cemented, porous calcarenite rock with a tendency to disintegrate), the following conservation problems have gradually affected not only the few remaining pictorial remains but also the very geometry of the funerary chambers:
-Runoff and rainwater infiltration phenomena.
-High relative humidity conditions.
-High light intensity due to excessive solar exposure.
-CO₂ concentration.
Based on the characteristics of the elements being intervened and the site conditions, the project sets out the following objectives:
-Enhancement of the archaeological ensemble under intervention.
-Integration into the landscape.
-Improvement of accessibility and access conditions to the tombs.
-Interpretation of the pre-existing features through the new projected elements.
-Effective protection of the tombs using sustainable, self-sufficient, and reversible procedures.
From the described objectives and the analysis carried out, the following strategies guide the proposed solution:
-A comprehensive canopy is designed to cover both tombs, creating a single, integrated ensemble. With sufficient height and curvature, it stands out only as necessary in the landscape, appearing as a piece of artificial topography that emerges to protect and support the contents of the tombs. The separation from the ground and the perimeter supports give the canopy the character of a temple that relates to the landscape, enhancing the heritage asset.
-The effect of the supports has been minimized, promoting the idea of free space and, in any case, integration into the natural environment of the site. Thus, the supports touch the ground with the least possible material, making it evident that the canopy is an independent entity rising from the terrain.
-A frieze is designed, resolved with plywood panels reduced to their minimal expression as a material and formal transition element between the supports and the canopy. This creates a smooth transition between the edge of the ensemble and the membrane roof. Its centripetal texture helps focus attention inward.
-Thus, the project reflects on what a contemporary architectural order should be like, optimized to produce the least possible environmental impact. To this end, it reduces the supports to their minimal expression and turns the frieze into a flat element, almost an aerodynamic disc, that resolves the junction with the two covering layers. The chosen geometry favors material reduction while reinforcing the idea of a small temple that protects and singularizes the ensemble.
-A new system of reversible walkways is incorporated to resolve accessibility to both tombs and enhance the interpretation of the Tomb of Postumio. Beneath the walkways, the ventilation system for the chambers to be conditioned is resolved.
To properly materialize the above, a parametric optimization process was developed based on the simulation of:
-Correct geometry for solar control, allowing sufficient radiation in cold seasons and completely blocking it in warm seasons.
-Optimized canopy geometry for external actions (mainly wind and snow) through control of the perimeter geometry, the curvature of the arches composing the canopy mesh, and the position of the supports.
-Air chamber thickness to control its effect as a thermal engine, achieving air in the best conditions for the site.
-Reduction of environmental impact throughout the building’s life cycle by imposing a lightweight, quick-assembly, reversible, recyclable system with passive conditioning strategies, low-consumption active elements, and self-sufficiency through on-site energy production.
The final solution is materialized, according to the developed models and plans, using the following elements, fully fabricated off-site in a workshop and assembled on-site with bolted connections, making it a completely reversible system:
01. Interface with the natural terrain consisting of ballast boxes resolved with S280GD steel sheet, 3.0 mm thick at the bottom and 4.00 mm thick for stiffeners and sides. Welded joints in the workshop. Connection node with CHS 80.3 structure, S275 J0, joined to 4.0 mm stiffeners.
02. Roof structure composed of a synclastic mesh of variable-curvature arches adapted to a four-sided perimeter with hyperbolic paraboloid edge geometry, resolved with reinforced Warren-type lattice. Slender supports stiffened with stabilizing crosses. The entire roof is resolved with CHS 70.3 S275 J0 tubular profiles and high-strength cables ∅12, 6×19+1 CF, 1770.0 N/mm².
03. Double envelope covering (outer roof and inner ceiling) resolved with 684 Polyplan All-In-One FR textile membrane by SATTLER PRO-TEX, with polyester warp and weft, PVC-coated on both sides. Different colors for the outer roof and inner ceiling to achieve proper integration with the surroundings.
04. Perimeter frieze of 15.0 mm plywood panels with exterior-grade paint compliant with CTE DB SE-M (high UV filter, high resistance to sun and weathering, waterproof and breathable. Fungicide and insecticide protection).
The canopy is truly a machine that integrates an active protection system (based on ventilation and air extraction elements) to maintain the hygrothermal conditions of the tombs at optimal values for their conservation. In the air chamber created between the two membrane layers that make up the canopy, an effective site protection system is integrated, consisting of:
05. Passive environmental control system based on 4 in-line ventilation units, equipped with air conduction systems with on/off dampers and flow regulation dampers, allowing the following air flow transfers: exterior–canopy air chamber and canopy chamber–hypogeum interiors in bidirectional sense. Monitoring system based on open-source domotic sensors powered accordingly, reading T°, RH%, CO₂ concentration, and atmospheric pressure every 5 minutes, enabling real-time adaptation of ventilation protocols to psychrometric variable readings.
As indicated, the ensemble is self-sufficient thanks to the incorporation of an on-site photovoltaic self-consumption system with grid feed-in to the Archaeological Complex of Carmona’s own network, with capacity to cover the low energy demand of the installed equipment.
Following the described process, the result is a project adapted and integrated into the site, with minimal materiality, industrialized, quick to assemble, reversible, recyclable, and energy self-sufficient. With this approach, its environmental impact is kept below 100.0 kg CO₂ eq.
"I learned from the trees to let the wind pass through."
Manoel de Barros.
