Stone or brick arches built into roman concrete vaults are called “ribs,” but unlike the ribs in Gothic vaulting the Roman ones are usually flush with the intrados and would not have been visible once the vault was decorated. Vaulting ribs often have been discussed in works on Roman construction, yet they have rarely been studied systematically in terms of form, use, and context. Many of the most authoritative scholars on the subject were writing at a time when a number of important monuments had not been properly dated or, in some cases, even excavated. Recent studies on individual monuments such as the Colosseum, the Forum of Caesar, Trajan's Markets, the Baths of Caracalla, and a series of late Roman domes need to be put into a developmental context before we can understand why the ribs were used and how they changed over time. The development of the ribs in vaulting is closely connected with the use of relieving arches over openings in walls, so the two techniques are discussed together.

In the past, scholars of Roman architecture have disagreed about the role that ribs and relieving arches play within the fabric of the concrete structure. Some have asserted that once the concrete cured, the relieving arch or rib became part of the hardened mass and no longer acted independently to divert loads or to reinforce the concrete, whereas others have assigned them a more active role in the channeling of loads through the hardened mass of the concrete even after the curing of the mortar.