Banded Barrel Vault
A technological improvement in Romanesque architecture was the banded barrel vault, which is a long barrel vault with transverse arch bands at regular intervals, figure 12. Fitchen provides a detailed explanation of the banded barrel vault. (Fitchen 1961, 46.)
Figure 12. Banded barrel vault diagram - Fitchen (1961, 46).
The arch bands are slender arches made of simple and uniform voussoirs, seemingly protruding down from the barrel vault. However, during construction they are the first elements to be erected, held in place by centering timberwork. Two such arch bands erected at a distance from each other serve as guides and anchor points for the barrel vault that spans over these arches.
This technique allowed a long barrel vault to be built in separate segments, bays. The challenge in building barrel vaults is that they have to be built in their complete length at the same time, before the vault masonry can take the load and the supporting timber falsework can be removed. Segmenting long barrel vaults thus simplified and modularized the construction process.
Arch bands segmented the construction of long barrel vaults as successive bays that were built separately and at different times, even years apart. More significantly, they divided and modularized the vault construction into separate and simpler constructions steps. The arch bands served initially as guides in erecting the barrel vault. Afterwards, they served as permanent armatures that reinforce the barrel vault. The arch bands also served to cover imperfections or differences between the barrel vault sections of adjacent bays, which would be exposed at the joint lines. Fitchen discusses in depth the banded barrel vaults and the role of arch bands. (Fitchen 1961, 47.)