What type of vault consists of a semicircular shape over a rectangular space?

The correct type of vault consisting of a semicircular shape over a rectangular space is the barrel vault. This architectural element is created by extending a semicircular arch along a given length, resulting in a long, tunnel-like structure.

The barrel vault is a fundamental component of Roman architecture and was widely used in various structures, such as basilicas and aqueducts. Its design allows for the effective distribution of weight, enabling the construction of larger and more stable spaces than was previously possible with simple post-and-lintel systems.

In contrast, a groin vault is formed by the intersection of two barrel vaults at right angles, creating a more complex structure. A basilica vault often refers to the design arrangement of successive barrel vaults within a basilica, while a dome vault typically refers to a rounded vault that rises from a circular base, resembling half of a sphere. These distinctions help clarify why the barrel vault is recognized specifically as the vault with a semicircular shape over a rectangular area.