On Gothic Cathedrals [again]

Quadripartite Vaulting

Another feature of Gothic Cathedrals, which makes their appearance distinctive, is the quadripartite vault. To full appreciate the impact of this innovation it is necessary understand what came before.

The first vaults are often attributed to the Romans, however both the Greeks and the Egyptians are known to have used them. Most early vaults were of the barrel variety, which is essentially a semi-circular arch extruded into the third dimension. The Chaldean version was formed of a series of arches inclined to one side. The inclined angle allowed them to be built without centring, assuming of course that the end was buttressed.

Masonry barrel vaults are useful for bridging long rectangular spaces, however they require heavy walls to support them due to the lateral thrusts imparted at their base. This is the same action that is found at the base of all arches and has been discussed in prior posts.

Since heavy walls were required to support barrel vault roofs it was difficult to fit large windows into the elevations. For this reason early churches constructed in this way were dimly lit. The Romans found an answer to this problem by interlocking barrel vaults in perpendicular directions. This concentrated loads at the junctions between vaults allowing them to be supported on large piers. The junctions between the vaults are known as groins leading to the eponymous name groin vaults. The obvious advantage being the ability to create windows in the elevations.

Groin vaults were structurally efficient, however they required very skilful masons to carve the groins’ complex geometry. For this reason they fell out of favour with the collapse of the Roman Empire.

Subsequently medieval masons introduced their own solution, which is known as the ribbed vault. Instead of constructing groins they bridged the building with a series of masonry ribs. Each bay had two diagonal ribs and three transverse ribs. This is known as the sexpartite ribbed vault, because the ribs divide the vault into six parts.

An advantage of this form is that load is concentrated at six piers, which means that, as with groin vaults, heavy walls were no longer required. Consequently, the space between the ribs can be used to form windows.

Since the ribs convey load to the supporting piers the infill between them need only span the short distance between the ribs. This was an improvement over the groin vault, which meant the infill could be both thinner and lighter. This in turn reduced the weight to be carried on the piers and also the magnitude of lateral thrust to be resisted.

One of the initial problems with sexpartite vaults was one of geometry. The span of the diagonal ribs is greater than the span of the transverse ribs. It follows that if the ribs are semi-circular in profile, like the barrel vaults from which they evolved, then the crown of the diagonals is necessarily at a different level to the transverse ribs. Masons solved this problem by using pointed arches for the transverse ribs. This meant that the level of their apex could be independent of their span. 

This innovation was also beneficial structurally. Since the inclination of a pointed arch is steeper than an equivalent semi-circular arch the magnitude of the resulting lateral thrusts is reduced, which also means the buttressing requirements are less.

Another problem with sexpartite vaults is that the intermediate piers carry less load than the diagonal ribs and this could lead to differential settlement. Medieval masons therefore began to omit the intermediate ribs. This had the advantage of concentrating both vertical loads and lateral thrusts at only four positions in each bay. It also limited the number of buttresses.

This new form of vaulting was known as the quadripartite vault, for the obvious reason that it was divided into four parts by the ribs. The effect it had on gothic architecture was profound. It led directly to the development of the flying buttress and also permitted spectacular windows to be constructed in the large spaces between ribs. Furthermore, the use of pointed arch ribs was instrumental in allowing cathedral roofs to be built ever higher. Not only did this lead to some astonishing spaces, but it was also of symbolic importance, as the resulting cathedrals were able to reach evermore heavenward.

 

The quadripartite vault was not the final stage in the long evolution of masonry vaulting, but it probably was the most definitive development. It is testament to the expertise of the Medieval Masons and the confidence they had to open up elevations to the extent that they did.

The legacy they have left remains with us to this day and will no doubt be with us for some time to come.