Cross Vault Arch Bands
Gothic architecture, known primarily for its unique forms and the iconic groin arches, was more than a stylistic development; it was an important technological improvement over Roman arch technology in the construction of cross vaults. Building upon the Romanesque achievements of banded barrel vaults, medieval architects transposed the concept of armatures made of stone arch bands to the construction of cross vaults, a natural evolutionary step.
Circular arch bands are much easier to build for a number of reasons. The voussoirs have fewer surfaces of much simpler shapes, and the circular arch bands have a uniform curvature, which result into voussoirs of identical cross section and curvature. The arch band voussoirs can be cut in the finished form at the quarry where all that is required is the cross profile of the voussoir and the radius of the arch. A lumber template cut to the shape of the arch can serve as a guide for the stone cutters. The result is a much simpler stone cutting and construction approach where the voussoirs are interchangeable along the arch.
Using two such stone arch bands to define the groins of a cross vault is therefore a much simple and faster stone cutting approach. These arch bands, intersecting at right angle, form the groin arches, the ribs. Built first and held in place by centering timberwork, the groin arches are the foundation for the vault webs, serving as permanent centering forms.
Fangari provides a graphical rendition of the erection of the arch bands for the diagonal and transverse arches, including the centering timberwork, figure 13.
Figure 13. Arch bands built first and serving as foundations for the vault webs – Fangari (2010, 14, figure 15).
This approach simplifies and modularizes the construction of cross vaults, eliminating the need for difficult-to-cut groin voussoirs and thus solving the challenge that restrained Roman cross vaulting technology.