Elevation of Bourges Cathedral

      Medieval archaeology should not be confused with the philosophy of art that is sometimes held up as its model and has at times been proposed as its ultimate goal.

History and Its Methods

In the preceding pages we have surveyed the floor plans; however, these are only one aspect of the problem. They are merely the shadow of immense structures reaching toward the sky. They are both the indirect consequence and the primary cause of these structures. One might say, in Aristotle’s sense, that the two are reciprocally architectonic. So, let us be curious and lift our heads to turn our attention to the elevations, which, without a doubt, embody the purest form of geometry.

The first cathedral featured on this site is Bourges Cathedral. Now is the time to discover its secrets and put into practice what we learned from Chartres (a study of Chartres is included in the book). The plan in Figure 1 is a laser scan, an elevation section of the nave of Bourges. We can see that the outlines of the floor plan have been projected vertically. These lines define the arrangement of the cathedral’s spaces: the central nave, the transepts, and the side aisles.

Fig. 1 - Elevation of Bourges Cathedral

Let’s begin by determining the point where the vault begins. To do this, I superimposed two equilateral triangles (Fig. 2). We can see that the method is identical to the one used to determine the profile of Chartres. The fact that a single outline can define both the structure and the profiles is revealing. It shows us that design methods were common to all Gothic builders and that they had universal applicability. Undoubtedly, medieval master builders were part of the same school and shared the same training.

Fig. 2 - Elevation of Bourges Cathedral (Step 1)

Let us now turn to the analysis of the interior profiles. As can be seen in Figure 3, the layout of the central nave consists of a long square (double square), as is the case with many cathedrals. The vault is traced by a line divided into five parts. We have studied this method previously.

 

Fig. 3 - Elevation of Bourges Cathedral (Step 2)

We now have the interior volumes of the cathedral as well as its layout. The following plate brings these systems together (Fig. 4). It is clear that these are the two complementary aspects of the monument’s design: the structure and the interior profiles. The lines of the polygons used are juxtaposed and merge into one another. This design is a true masterpiece.

Fig. 4 - Elevation of Bourges Cathedral (Step 3)

Without the reference points provided by the triple enclosure, it would be impossible to know how to position the volumes in relation to one another. The role of the segments is to simplify this construction. But in practice, how did the architect transition from the first system to the second? Indeed, a common value is needed—a link that unites them. We have seen that the height of the central nave played this role. Once determined using the method shown in Figure 2, this height is divided by two to form the two superimposed squares of the central nave (Fig. 3).

As for the side aisles, they consist of three superimposed squares, the whole of which is topped by a further 2/3 projection. The vault is drawn as a pointed arch (based on an equilateral triangle), just like those of the side aisles. Note that the height of these same side aisles aligns with the first square of the side aisles.

It is important to understand that the horizontal difference between the green line (the layout) and the yellow line (the profile) is equal to half the width of the piers. It is therefore very easy to determine the width of the piers. This ratio is represented by the white circle. The elevation has now been redrawn. The remaining structures—flying buttresses and other masonry units—are calculated on a case-by-case basis.

Credits: The scan used here comes from a document provided by Andrew Tallon to Professor Robert Bork for his article “The Geometry of Bourges Cathedral” under a CC BY license. The document has been converted to negative to improve readability.