Noun
the simplest form of vault; a single continuous arch
Source: WordNetBarrel vault The simplest type of vaulted roof is the barrel vault in which a single arched surface extends from wall to wall, the length of the space to be vaulted, for example, the nave of a church. Source: Internet
However, the barrel vault generally required the support of solid walls, or walls in which the windows were very small. Source: Internet
The barrel vault is returned to architectural vocabulary as at the St. Andrea in Mantua. Source: Internet