Oecus

Oecus is the Latinized form of Greek oikos, used by Vitruvius for the principal hall or salon in a Roman house, which was used occasionally as a triclinium for banquets.

House of Augustus, south wall of the "Large oecus" with frescoes in the Pompeian Style, Palatine Hill, Rome

When of great size it became necessary to support its ceiling with columns; thus, according to Vitruvius, the tetrastyle oecus had four columns; in the Corinthian oecus there was a row of columns on each side, virtually therefore dividing the room into nave and aisles, the former being covered over with a barrel vault. The ancient Egyptian oecus had a similar plan, but the aisles were of less height, so that clerestory windows were introduced to light the room, which, as Vitruvius states, presents more the appearance of a basilica than of a triclinium.