The boldness of the builders still commands respect to Construction techniques. How did the men of the Middle Ages dare to launch such stone arrows towards the heavens? Their empirical and geometric approach defies the calculations of today’s architects. Strasbourg Cathedral is a very well-documented building. The study of its history gives us precious elements of the techniques of the builders.
The art of construction cannot conceive without geometry. The fundamental constraint of a building, gravity, defines the two axes of an elevation: upright, vertical, and level, horizontal. From the first uplifts, this is imposing on men. On the other hand, the geometry is also having for object the proportions. It presides since Antiquity with the “Construction techniques of the beautiful.” By relying on specific geometric rules, often anthropometric. It is possible to design an object “on a large scale,” which is pleasing to the eye.
The square and the triangle and the circle
Probably based on empirical results, the principle seems accepted in the Middle Ages: to remain stable, you have to be square. The location of the buildings on the ground has followed this logic since Antiquity. We speak of construction ad quadratum, according to the courtyard.
On the other hand, the different fundamental geometric shape in architecture is the triangle. It is mechanically unreformable. That is why, even today, vertical structures, such as frames or scaffolding, are triangulated. It is the construction ad trigonum, according to the triangle.
Elevations of the arches
The circle intervenes in the layout of the elevations of the arches and vaults the plan of the towers.
By combining these principles, geometry becomes the key to the science of builders. That naturally results in a specific language, which will take on symbolism over the centuries.
The knowledge of the ancients
So even the architectural designs did not appear before the XII and XIII centuries, the building of house drawing trace on the ground. The churches are traditionally oriented, that is to say, oriented towards the East of the heavenly Jerusalem. The builders probably established the Construction techniques axes thanks to gnomonic, the science of solar orientation known from Antiquity.
The regulating routes
From this axis, the plan of the building is brought, probably from a square, which will develop in a more complex form, but geometrically coherent: the regulating route. This process is not systematically proven nowadays, but its practical relevance is essential.
The builders use tools inherited from the great scientists of Antiquity, such as Pythagoras or Thales. The most emblematic example of this heritage is the famous thirteen-knot rope, a geometrical instrument on the scale of the construction site.
The cathedral builders
In the Middle Ages, the architect of a building is often a stonemason who, by dint of experience and intellectual curiosity, becomes prime contractor, the building designer, and custodian of Building Sciences.
Under the aegis of the project manager attached to the building, a team of highly qualified craftsmen is forming. They are probably itinerant workers, following the master at the discretion of the sites. These craftsmen organize in lodges that establish the statutes and the operating rules.
The construction of a cathedral
The Construction techniques of a cathedral spanned several centuries. The craftsmen who follow one another on the site influence each other and pass on techniques and fashions across Europe. The one scholar sketchbooks, perhaps prime contractor for the XVIII century, have survived. They attest to this wealth through the Gothic works of its time. These are Villard de Homecourt. Probably a scholar initiated into the trades of builders.
The medieval construction sites
The established foundations are built, more or less imposing according to the height of the wall envisaged—those of Notre Dame de Strasbourg date from 1015. The first foundations of stones raise. As the Construction techniques progress, the wooden scaffolding rises. Indeed, it is the walls that carry the medieval structure through the bowling holes. The boudins, horizontal beams crossing the masonry right through, have a scaffolding floor on each side of the wall.
As the building emerges from the ground, the cladding of materials (stone, wood, mortar) requires lifting gear. These machines naturally use human energy, as shown by the big squirrel wheel or the capstans of the cathedral. The keystones are placing on a hanger to form the arches and vaults. In the case of large bays, the lattice likely plays the role of a permanent hanger.
The sketchbooks of architect
The sketchbooks of architect Hans Hammer are a precious testimony of these machines. The gripping of the stones is ensuring by the claw, at other times, by the wolf. Both methods have left their mark on the facings of the building. Most of these medieval techniques are still using today. Moreover, the stones are still sealed today as at the time, with lime mortar or lead.
With the advent of the novel, then the Gothic, the art of the line develops. The design allows the project manager to be more daring in his projects. Strasbourg Cathedral and its spire are a perfect example of these developments.
The ambition of the Gothic style is to rise as high as possible towards the heavens. This concern for verticality implies reducing the weight and thickness of the supports (walls and pillars) without compromising the stability of the structure. The system of buttresses in the buttress will relieve the walls by absorbing the pressure of the vaults.
As a result, the bays enlarge, ribs are more resistant to stress replace the semicircular arches. The high windows become monumental and are adorning with increasingly rich stained glass. The wall’s apparent lightness is reinforcing by a system visible in the western massif of the cathedral: the mighty walls of the shell hide a curtain of stone lace.