The stereotomy of complex surfaces in French Baroque architecture

The term Baroque supposedly comes from the word used to describe irregular, misshapen pearls. There is indeed a very special beauty in the stretched stones of elliptical domes, in the warped surfaces of spiraling stairs, in the blooming shapes of vaults. Supported by developments in mathematics and geometry, the high renaissance and Baroque periods produced some fascinatingly complex works such as Philibert de l’Orme’s squinches or Hardouin Mansart’s vaults.

Thinking of the incredible task of building these irregular forms out of individual stones is dazzling. Looking carefully, one’s eye can follow the subtle and intricate web of the joints interfacing the panels, each one having its own unique shape interlocking into the other to create a continuous yet vibrant surface.

These joints lines are very interesting; they embody not only geometry, mathematics and construction, but also rhythm, ornament, haptic qualities and expressivity. They are at the same time abstract and sensual. They are the artifacts of the geometric manipulations through which it was possible to tessellate the overall form and determine the contour of the blocks.

The hinge that we are experiencing today in geometric description tools (from 2D drawings to the virtual three-dimensional space) is not without parallels with the development of the projection system of the stereotomical drawings (épures) that implemented the realization of some of the complex masterpieces of the Renaissance and Baroque period. Stereotomy was then at the very edge of architecture.

Philibert de L’Orme

In the second phase of my project, I visited buildings by three French architects known for their use of steretomic techniques.

As a character of transition between Renaissance and Baroque, the works of Philibert de L’Orme was one of the focuses of the field trip. His work is crucial to this project because of the direct link between theory and practice in his work. One of the two surviving buildings has elements typically representative of his use of projective geometry to create complex forms. In Lyon, the Hotel Bullioud (1536) features two squinches (trompes) and the difficult “screw of Saint-Gilles” cut of the spiral stair. Also, the Anet Castle (1547-55) where I analyzed the delicate interlaces of the porch’s vault and the chapel’s cupola.

Philibert de l’Orme was born in 1514 in Lyon. His father was a master mason himself and Philibert worked on construction sites from a very young age. At fifteen years old he was already in charge of 300 masons on a construction site in Lyon.

Ten years later, at the peak of his career, De l’Orme caught the attention of King Henry II with the St-Maur Castle (1541-1544) for the Cardinal du Belley. He had been appointed as the Fortifications Inspector of Brittany in 1545 and he would become the King’s Architect in 1548. Henry II started the construction the Anet Castle to house his Mistress, Diane de Poitier.

Originally a large construction organized in three wings around a central courtyard, the castle was partially dismantled after the French revolution in order to sell the stones. With this demolition one of the masterpieces of the French stereotomy disappeared, the famous Anet Squinch. Remaining today are the gate building, the chapel, one wing of the castle itself and the funerary chapel of Diane de Poitier.

Although they do not involve any special stereotomic techniques, the delicate lacework of the railings are to be noted. De L’Orme uses a vegetal lacework pattern again in the barrel vault of the porch. It is very interesting to note how the construction and ornamentation are synchronized by de l’Orme. Since there is no plaster work or any added stone ornamentation over the load bearing stones, the pattern needs to be engraved directly in the same stones that are composing the structural arch. The panellization of the vault thus has to be thought of at the same time as the ornament to avoid having the joint cutting in the wrong place in the pattern.

Similarly to the barrel vault of the porch, the cupola of the chapel shows how the constructive and ornamental orders are closely intertwined. Each horizontal course is composed of only one bloc that is repeated (upside-down every other repetition). Even with these limited means, the progressive variation in size towards the top creates a rich spiraling effect.

The diminution in size of the pattern towards the top plays with the perspective and gives the impression of a stretched dome much higher than the half-sphere it is in reality.

François Derand

François Derand (1588-1644) was a Jesuit priest at La Flèche where he learned architecture under Etienne Martellange. He worked on or consulted for various projects, among which are the Orléans Cathedral, the Rennes College and the La Flèche Church. He was called to work on the Saint-Paul Saint-Louis Church in Paris in 1629, a project started by Etienne Martellange.

It is interesting to note the absence of ribs reinforcing the corners. The gothic technique usually consists in building the structural ribs first and then filling the surface with stones. The infill stones are acting structurally as a diaphragm but not so much taking the compressive load. With stereotomic techniques, the precise cutting of the stones prior to their assembly made it possible to avoid the ribbing and make a uniformly structural vault. Derand took the model for St-Paul St-Louis on the La Flèche church, by Martellange, but eliminated the ribs to make a ‘‘naked vault’’ showing the joints pattern and the smoothness of the surface.

Jules-Hardouin Mansart

In 1673, many architects proposed new plans. The various projects all featured intermediary columns in the center of the space. Plans by Dominique Pileporte were finally approved. The new foundations were finished quickly but the council, learning that Jules-Hardouin Mansart was in a town nearby, sought his advice on the project.

Mansart studied the project and made a daring proposal. His plan would completely eliminate intermediary support. With the shallow possible depth of the vault covering the hall, this would be an exceptional structural feat. His plans were finally approved by the council and the construction moved forward.

The most notable aspect of the vaults is the meticulously planned layout of the stones’ rows. The joints lines echo closely the shape of the vaults, changing directions according to the ridges and breaks of curvature.

Conclusions

After the study of the evolution of his various squinches, we can say that de l’Orme really used the geometric drawings as a mean to create original things he could hardly envision without. As Robin Evans put it in his book on geometry in architecture, ‘‘The shape of the trompe was not merely falicitated by projection drawings, but generated by it.’’

On the other side, François Derand used stereotomy mainly to perfect the construction of a known typology initiated by Etienne Martellange. Where the Martellange vaults at La Flèche were full of visible knuckles and discontinuities, those of Derand in St-Paul St-Louis were smooth and straight, this even after having removed the structural ribs Martellange had previously.

Hardouin-Mansart is a bit of a mixed case. Altough he clearly not had the type of experimental relationship with drawing de l’Orme had, we can feel that the vaults of the Arles Town Hall are the result of the intersections of the various elevations of the hall, creating unexpected arcs and curves where the vaults are intersecting in space.