Clerestory (IPA: /ˈklɪə(r)stɔəri/; lit. clear storey, also clearstory, clearstorey, or overstorey) is an architectural term enoting an upper level of a Roman basilica or of the nave of a Romanesque or Gothic church, the walls of which rise above the rooflines of the lower aisles and are pierced with windows. The Romans also used clerestories in their basilica-like baths and palaces, and probably derived the clerestory from the Hellenistic architecture of the Greeks. The clerestory originated in the temples of Egypt. It is also used to denote a style of railway rolling stock (predominantly passenger), for example the Great Western Railway Clerestory carriage of the Victorian era where the windows in the roof 'cupola' provided access to, and ventilation for, the vehicle's gas lighting.