In architecture, an atrium (plural: atria or atriums) is a large open-air or skylight-covered space surrounded by a building.Atria were a common feature in Ancient Roman dwellings, providing light and ventilation to the interior. Modern atria, as developed in the late 19th and 20th centuries, are often several stories high, with a glazed roof or large windows, and often located immediately beyond a building's main entrance doors (in the lobby).