the.com/barrel vault

means An arched roof or ceiling shaped like a continuous half-cylinder, formed by extending a single arch profile along its length to span a space without internal supports.

from The architectural sense comes straight from the shape: a row of wine barrels lying on their sides, their curved staves tracing the same continuous arc you see overhead in these structures. 'Vault' itself descends through French 'voute' from Vulgar Latin 'volvita,' tied to 'volvere' — 'to turn or roll' — the same root family that gives us 'revolve' and 'volume.' So the word is doing double duty: 'vault' already carries the idea of a turning, rolling curve, and 'barrel' just nails down which curve, borrowing the cooper's familiar cask shape to describe what masons had been building since Roman times, long before anyone called it that.