In plan (Wikipedia) the belt arches are shown in green; the red area is part of a travée (bay).
A belt arch carries the roof construction of a church.
The picture shows several belt arches in the Saint-Martin in Chapaize.
The arc (arch) in the foreground is strictly speaking not a belt arch; it carries also part of the coupole (cupola) under the clocher (bell tower), and hence part of the clocher as well.
See also doubleau (synonym).
|Arc-doubleau - Wikipedia|
|Saint-Martin - Chapaize|