When the arch is extended in depth—when it is, in reality, many arches placed flush one behind the other—the result is called a barrel vault. This vault construction makes it possible to create large interior spaces. The Romans made great use of the barrel vault, but for its finest expression we look many hundreds of years later, to the churches of the Middle Ages.
The church of Sainte-Foy (13.10), in the French city of Conques, is an example of the style prevalent throughout western Europe from about 1050 to 1200—a style known as Romanesque. Earlier churches had used the Roman round arch to span the spaces between interior columns that ultimately held up the roof. There were no ceilings, however. Rather, worshipers looked up into a system of wooden trusses and the underside of a pitched roof (see 15.2, 15.3). Imagine looking directly up into the attic of a house and you will get the idea. With the Romanesque style, builders set a stone barrel vault as a ceiling over the nave (the long central area), hiding the roof structure from view. The barrel vault unified the interior visually, providing a soaring, majestic climax to the rhythms announced by the arches below