Silos dits Greniers de César
MonumentHidden Treasure
Enigmatic underground silos dug into the Amboise tufa stone, these four 16th-century cylinders with their hemispherical domes conceal an ingenious conservation system with two levels of galleries.
© Wikimedia Commons
History
Nestling in the tuffeau hillside beside the Loire at Amboise, the Greniers de César are one of the most unusual underground structures in Touraine. A far cry from ordinary granaries, these four cylindrical silos topped with hemispherical domes reveal a remarkable constructive ingenuity: each is insulated from the rock by a layer of sand and clad with a brickwork of small bricks, forming a natural thermal enclosure of rare effectiveness. The entire structure, carved out of the volcanic molasse that is so characteristic of the region, bears witness to a level of technical expertise that is in no way inferior to surface architectural achievements. What makes this site truly exceptional is the superimposition of its spaces: a lower gallery some one hundred metres deep, an intermediate gallery whose broken vaults still reveal the presence of a former floor, and finally the silos themselves, accessible from the upper level via circular openings. At the centre of each silo, a rectangular shaft plunges down to the lower gallery, forming a ventilation and humidity control system of astonishing sophistication for its time. Visiting the site is like plunging into the bowels of the Loire hillside, far from the hustle and bustle of the banks of the Loire. The constant coolness of the galleries, the tufa stone that absorbs the artificial light giving it a golden hue, the muffled echo of footsteps on the rocky floor: everything contributes to a timeless atmosphere. The straight staircase carved into the rock, linking the different levels, gives the place the solemnity of an underground sanctuary. The setting is doubly remarkable: these underground passages are now part of the grounds of the hotel-restaurant Le Choiseul, a luxury establishment whose terraced gardens overlook the Loire. The confrontation between the hotel's classical elegance and the primitive brutality of these tunnels dug into the tufa stone creates an unexpected architectural dialogue. Just a stone's throw from the Royal Château of Amboise and Leonardo da Vinci's house at Clos Lucé, Les Greniers de César offers an unusual and little-known facet of the royal city of the Renaissance.
Architecture
The architecture of the Greniers de César is entirely underground, organised according to a rigorous vertical logic over three distinct levels. At the base, a lower gallery on a level with the inner courtyard extends for around a hundred metres into the depths of the hillside, forming the backbone of the system. Above this, an intermediate gallery with a vault that has disappeared - all that remains of it are the tears in the rock - once divided the space into two distinct levels. It is on this intermediate level that the four silos nestle, once hermetically separated from each other and now linked by openings in the walls. Each of the four silos has the same shape: a vertical cylinder topped by a hemispherical dome, reminiscent on a small scale of the grain tanks of Mediterranean antiquity. Their construction reveals a highly refined technique: far from simply being dug into the tufa rock, they are lined with a brickwork of small bricks that is not laid directly onto the rock but is separated from it by a gap carefully filled with fine sand. This double wall creates remarkable thermal and hygrometric insulation, maintaining stable conditions inside that are ideal for conservation. The top of each dome is pierced by a circular opening, located at floor level on the upper floor, which served both as access to fill the silo and as a light or ventilation shaft. In the centre of the floor of each silo, a rectangular shaft cut into the rock leads down to the lower gallery, completing the natural ventilation system. A straight, monolithic staircase carved directly into the hillside provides access between levels - a solution that is both economical and austerely troglodytic in its elegance.
Related Figures
Gastignon, apothicaire d'Amboise, aménageur des silos en 1548François de Paule, fondateur de l'ordre des Minimes, lié au monastère d'Amboise (1491)Charles VIII, roi de France, fondateur du couvent des Minimes d'Amboise (1491)Les Minimes d'Amboise, propriétaires des souterrains de 1588 à la Révolution
