With pozzolan cement enabling Roman concrete, interiors achieved large spans with which structural system?

• A. Arch and vault
• B. Post-and-beam
• C. Barrel vault only
• D. Wooden trusses

Answer: (A)

Pozzolana cement makes hydraulic concrete that can harden and set in larger, more complex forms. This enabled Roman builders to create wide, open interiors by using arches and the vault, which efficiently carry loads and direct them to strong supports. An arch converts vertical loads into horizontal thrusts that are transferred outward, allowing a wider opening than a solid wall could support. When arches are built in two directions or combined, they become vaults—cross, groin, or domed vaults—creating expansive interior spaces like those in baths, basilicas, and the Pantheon. Timber frame systems, or wooden trusses, aren’t what delivered these large, durable interior spans in Roman concrete. A single barrel vault can span but doesn’t offer the same broad interior openness, whereas the arch-and-vault combination provides the practical means to cover large areas with fewer supports.