What is "cryptoporticus"

n. (''in Roman architecture'') A vaulted corridor or arcade at, or just below ground level; normally lit by openings in the upper part of the vault. Also a roofed promenade that is enclosed with side walls that have windows or openings instead of columns.

In Ancient Roman architecture a cryptoporticus (from Latin crypta and porticus) is a covered corridor or passageway. The usual English is "cryptoportico". The cryptoportico is a semi-subterranean gallery whose vaulting supports portico structures aboveground and which is lit from openings at the tops of its arches.

On sloping sites the open side of a cryptoporticus is often partially at ground level and supports a structure such as a forum or Roman villa, in which case it served as basis villae. It is often vaulted and lit by openings in the vault. In the letters of Pliny the Younger, the term is used as a synonym of crypt. The shade and semi-excavated site of a cryptoportico provided cool and moderated temperatures useful for storage of perishables, while it offered a level and slightly raised podium for the superstructure.