The Église de la Sainte Trinité is one of two abbey churches built by William the Conqueror and his wife Matilda in Caen. Our last post discussed William and the Église Saint-Etienne, the Abbaye aux Hommes. La Trinité, or the Abbaye aux Dammes, is featured this week, but the post is less about history than some very interesting architectural features.
Both churches were started in 1059 and were built in classic Norman Romanesque style – virile, intelligent, with little ornamentation but with beautiful “bones”. The apse of the Abbaye aux Dames is a marvelous creation. It stands proudly over Matilda’s crypt with sixteen piers in four rows on two levels, covered by a painted oven vault.
Each of the churches was originally covered with a timber roof. At the end of the first quarter of the 12th Century, the wooden roof was replaced with a stone vault. Because the original walls of these churches were not designed to carry the weight of a stone vault, the builders were forced to make two fundamental adaptations. The first was a departure from the conventional barrel vault and the second was to support the original walls.
To solve the vaulting problem, the builders decided to experiment with the groin vault. The groin vault is a significant improvement over the barrel vault because the thrust is not directed to the supporting walls along the entire length of the vault, but only at the intersection of the vault ribs and the walls. The difficulty with a groin vault is that it can only span a square volume because it is necessary for the arches to rise to the same height. Since the width of the nave was twice the width of each bay, the groin vault had to span two bays in order create a square volume. This was a challenge – the weight of stone would certainly threaten to collapse over such a span.
In order to add support, the builders of both churches decided to add a supporting span from the two intermediate pillars, but they did it in different ways. In the case of the Abbaye aux Dames, they came up with a highly original design – the pseudo-sexpartite vault featuring a diaphragm arch which served as a transverse load-bearing arch.
You can see the diaphragm arch very clearly in this following shot – it supports the center of the groin vault.
The next shot shows the vault directly from below and one can see that the square vault is divided into six sections by the ribs of the groin vault and the diaphragm arch – making it sexpartite. Without the diaphragm arch the groin vault would only have four sections. Because the diaphragm arch is not really part of the vault, but a support for it, this vault is called a pseudo-sexpartite vault.
The Abbaye aux Hommes came up with a different, and probably more sophisticated solution, the true sexpartite vault. Here, the transverse arch is a true rib spanning from the intermediate piers through the center of the groin vault. Since the distance that this rib spans is less than the diagonal distance spanned by the ribs of the groin vault, it rises to the center height at a greater angle. This creates a warp in the webbing, which makes the vault even stronger. This warp can clearly be seen in this photograph.
It is clear that these two sexpartite solutions were the precursors to the Gothic quadripartite vaulting. The vaults allowed a reduction in the thickness of the stone walls, creating a frame for the glass windows which are the glory of those cathedrals.
Having come up with a solution for the vaulting, the builders then had to address the problem of buttressing the original walls where the ribs intersected the walls. The builders of the Abbaye aux Hommes used a pre-existing expedient – they mounted half-barrel vaults over the side aisles. The curved surface supported the wall along the length of the vault.
But the continuous thrust of that half barrel vault placed a powerful stress inwards on the nave walls, and only the great strength of the seven-foot thick original masonry prevented the collapse of the walls.
This fault was corrected in Abbaye aux Dames. To quote Sartell Prentice, “Here the dangerous inward thrust of the half-barrel vault was avoided by cutting out the part of the side-aisle vault which lay between the piers, leaving only those sections of the buttressing vault which met the outward thrust of the nave vault above the piers. The result was the reduction of the half-barrel vault to a series of quarter round arches which were braced on the one side by the exterior walls, and on the other side by the lateral thrust of the nave vaulting.”
These quarter-round arches are really the precursors to flying buttresses. In both churches, this buttressing is invisible to the visitor – hidden out of sight above the roofs of the side aisles, but structurally, they serve the same function as their subsequent Gothic counterparts.
There is an interesting piece of chronology when comparing the two churches. It appears that the stone vaults were placed on both structures at approximately the same time. However, the vaulting itself is more advanced with the true sexpartite vault in Saint Etienne compared to the pseudo-sexpartite vault in La Trinité. But the half-barrel buttressing of the Abbaye-aux-Hommes is more primitive than than the quarter-round arches in the Abbaye-aux-Dames. This suggests that there were a number of movements taking place simultaneously and the lessons that resulted in the creation of Gothic architecture were still being developed. Suger’s Saint Denis was consecrated in 1144, just 20 years after these vaults were erected in Caen.
To me it is clear that the experiments in vaulting in Caen resulted in architectural solutions that were recognized for their structural innovations by those master builders who built the Gothic masterpieces of Europe. The Norman style spread to England and flourished there as both Romanesque and Gothic.
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