Buttress your knowledge! The wonderful world of medieval vaults

By Jo’anne van Ooijen

Medieval architecture offers a treasure trove of beautiful vaults that are often impressive feats of architectonics. Vaulted ceilings are art as well as engineering, combining attractive visual designs with structural ingenuity. But looking up at one of those intricate designs can be a challenge – how do you recognize which type of vault you are looking at and understand the structural logic behind it? This is where a crash course in deciphering vaults may come in handy.

Vaults are arched types of ceilings, whether constructed in stone, brick, wood, or other material. Vaults can be found in civic as well as religious buildings, but the development of vaulting in the European Middle Ages was moved forward mainly by the challenges encountered in a church building. We can distinguish four broad categories in vaulting, each with variations.


Barrel Vaults

The most straightforward is the barrel vault. Barrel vaults were already being constructed in Mesopotamia, ancient Egypt, and ancient Greece. Roman examples can be found in Hadrian’s Villa, the basilica of Maxentius, and the Roman sewer cloaca maxima. The technological knowledge for building barrel vaults was never lost, but for several centuries after the Roman period they were not executed on a monumental scale – until the Romanesque period.

Also called a tunnel vault or wagon vault, the barrel vault is constructed like a large arch that is extended longitudinally. Usually, barrel vaults have semi-circular ceilings, resembling cylinders that are cut lengthwise. A variation is the pointed barrel vault. While a vault is still under construction, it needs to be supported by temporary scaffolding, usually made of wood. Once it is closed by the uppermost keystone, the wedge-shaped stones push each other into place, similar to the construction of arches.


Palace of Diocletian, Split, Croatia. Basement room of Diocletian’s Palace, barrel vaulted ceiling – photo by Gaius Cornelius / Wikimedia Commons

The weight of the vault pushes downwards and outwards. It is carried by the walls, that transfer the weight downwards. Unless the walls are very thick, or the outside walls are supported by adjacent structures or vaults, a solution must be found for the lateral thrust. This can be resolved by adding buttresses against the outside of the walls to bear the outward pressure. When the walls of a barrel vault are closed, they resemble a tunnel. The walls can be opened up by arches, creating a division in bays, but this makes the issue of thrust more problematic.

Cross Vaults

A single barrel vault is not intersected. When two barrel vaults cross, a cross vault or groin vault is created. At the point of intersection, the ceiling forms the shape of an X. The weight of the intersection is distributed towards the four corners of the cross, and from there, over the four piers that carry the vault. Because the thrust is directed mostly downwards, the cross vault is structurally stronger than the barrel vault. Like the barrel vault, the cross vault can also be rounded or pointed.

Cross or Groin vault in the abbey church of Mozac. The aisle of the Abbey Church at Mozac has groin vaults supported on transverse arches – Photo by Jochen Jahnke / Wikimedia Commons.

Rib Vaults

The third category is the rib vault, or cross-rib-vault. At first glance, this looks like a cross vault, but the rib vault is more elaborate. Its surface is composed of arched compartments, divided by ribs that can be further emphasized by ridges. These ribs take over part of the weight, so that the rib vault offers the possibility of covering larger spaces and opening up walls. The ribs also allowed for thinner, lighter material to be used for the compartments, so the weight of the vault could be (somewhat) diminished. The pointed rib vault especially allowed for new heights to be reached, literally and figuratively, in architectural designs. It was part of the innovative leap that made the awe-inspiring, gravity defeating Gothic cathedrals possible.

Reims Cathedral – Photo: Josep Renalias / Wikimedia Commons

But the downward, and especially outward, pressure remained a serious structural challenge. While cathedrals became higher, at the same time, the wish to open up more of the wall surface for windows increased, to allow more light to flow in. The theological idea of God as light posed the challenge of creating ever higher, lighter, yet still stable buildings. So, although the rib vault has important structural advantages to the barrel vault, the need for buttressing remained: while the barrel vault calls for buttresses to sustain an excess of lateral thrust, buttressing in the Gothic period was needed mainly to compensate for the fragility of high walls with large stretches of glass.


Buttresses changed appearance with the shift from the Romanesque to Gothic style. From heavy, rounded and unadorned, they gradually became more elaborate, with sculptures for decoration and pinnacles for extra downward weight. When they are placed at a distance from the wall and bowing towards it, like giant legs, they are called flying buttresses. Buttresses can be placed on the ground, supporting the outer walls, or on top of side aisles, supporting the nave.

Flying buttress of Reims Cathedral, as drawn by Villard de Honnecourt – Bibliothèque nationale de France MS Français 19093. fol. 32v

Returning to the rib vault: many variations exist, for instance, the sexpartite rib vault. Six curved compartments cover not one, but two bays, distributing the weight over a larger number of pillars or columns. The outer ends of the sexpartite vault are marked by transverse ribs. Sexpartite vaults can either rest on a row of equal columns, or a more intricate bay system can be created: when the transverse ribs are carried by extra heavy pillars or piers, the result is a ‘rhythmically alternating bay system’. This means bays are separated by alternating a column and a heavy pillar. This gives a visual that can be used as a clever solution to match a wider nave to narrower aisles.

A more complicated type of rib vault is the fan vault. This is composed of concave compartments with ribs that spread out in the shape of a fan. Myriad elaborate varieties exist from the periods of the Rayonnant (ca.1300) and Flamboyant Gothic style (as of ca.1350).

Fan vaulting over the nave at Bath Abbey, Bath, England, Photo by Arpingstone / Wikimedia Commons

While the cross and rib vaults gradually evolved, the domed vault was already built-in both western and eastern cultures. This fourth category of vaulting has not been in continuous use, because the advanced technological knowledge needed for its construction was not always available, and large resources are necessary for its execution. Nevertheless, a wealth of variations exist, especially in the medieval Byzantine and Islamic world.

The domed vault is usually employed in a centralized building plan. When placed above a cylindrical space, such as the Pantheon in Rome for example, the dome follows the circular ground plan and no adjustments between wall and dome are needed.

Entering the Pantheon – photo by Neil Cornwall / Flickr

However, when placed above a cubical, rectangular, or other space, some sort of transition is required between the circular dome and the square plan of the walls or pillars on which the dome rests. This is usually solved by adding pendentives in the four corners. Note this subtle distinction: when the dome itself has four arches, creating four points on which it can connect directly to a square plan, it is called a pendentive dome. But when the dome itself has no arches, but rests on a substructure (like one scoop of ice-cream pressed on top of another) that has arches and pendentives in its turn, this is called a dome on pendentives. One of the most impressive examples is the central dome of Hagia Sophia in Istanbul. Its central dome on pendentives is flanked and supported on two sides by additional pendentive half-domes.

To support this massive structure, Hagia Sophia has a set of buttresses against its exterior walls that are among the largest in the world. The construction of Hagia Sophia is a tale in itself… for another time. For now, you are armed with the basics to identify vaults, understand how they work and enjoy their beauty even more.


Jo’anne van Ooijen studied Art History at Leiden University and International Law at Maastricht University. She currently works for the Council for the Judiciary in The Hague. You can follow her research on

This article was first published in The Medieval Magazine – a monthly digital magazine that tells the story of the Middle Ages. Learn how to subscribe by visiting their website.

Top Image: Line art drawing of an aisle – Wikimedia Commons