In architecture, which vault type is formed by the intersection of two barrel vaults at right angles, creating an X?

• A. Cross vault
• B. Groin vault
• C. Barrel vault
• D. Dome

Answer: (A)

When vaults are formed, the shape and how they intersect tell you what they’re called. A cross vault describes the result when two barrel vaults—long, curved ceilings like a tunnel—meet at right angles. Their intersection lines form a distinctive X, with the curved edges called groins. The space created is known as a cross vault (also called a groin vault in many texts). Structurally, this arrangement concentrates the weight along the groins and directs it to the supporting piers at the corners, allowing wider and more open bays than a single barrel vault. This is different from a dome (a hemispherical ceiling) or a pure barrel vault (just one curved tunnel). The groin vault term describes the same intersection, but the X-shaped pattern shown in the question is most specifically identified as a cross vault.