ATRIUM (Lat., a hall; literally, 'dark room,' from ater, black, dark, referring to the smoke from the stove or hearthstone. See below). In Roman architecture, the one large apartment of the primitive Italic and Roman house; the general room which served for kitchen, dining-room, reception and sleeping room. In it was the hearthstone, and the nup tial couch remained there as a symbol, even after the addition of bedrooms around it. As the Roman house became more sumptuous, small rooms were multiplied around this central hall, which remained immediately opposite the en trance, and then took the name also of catue divm. There were different kinds of atria : (1) The earliest kind, with the solid roof (atrium test udinat um) ; (2) next, the Tuscan atrium (tusranieum), which became the national type before the close of the Republic, with a square opening (compturivin) in the centre for ad mitting light. The roof sloped inward, so that rain-water flowed into a basin (im pia Hum) be neath the opening. With the enlargement of house and atrium came (3) the tetrastyle atrium (tetras, yl am) , with four columns sup porting the central opening; and finally, with the further sumptuousness of the times of Cicero and Augustus, came (4) the Corinthian atrium, where the four columns are multiplied into a real colonnade; and in this form the atrium is in distinguishable from a peristyle court, a private cloister. There was another early kind of atrium, used especially for winter apartments, in which the roof slanted upward like our roofs, instead of downward toward the centre, and shed the water instead of collecting it (displuviat um) . The patrician and richer
equestrian houses of the late Republic and Em pire usually had two atria—first the old-fash ioned kind (1; 2), for the transaction of busi ness, and in front of it the shops; and beside and beyond it, the aim and tablinum ; then a peristyle atrium, with columns, with rooms opening on to it, where the family life was curried on. The later atria were beautifully decorated with fres coes and sculptures, vases and fountains. The best-preserved atria of all kinds are in the houses of Pompeii. The term was also some times used of religious or public buildings, in the form of courts, such as the Atrium Vestae, attached to the house and temple of Vesta, and the Atrium Liberatis, which contained the first library founded in Rome.
In Christian antiquities, the atrium was a large columnar open court in front of the basili cal churches, used for meetings or promenades, and even for agapm and fairs. In the centre stood the fountain for ablutions. In it gath ered the penitents who were not allowed in the church. These atria went out of use in the early Middle Ages. Those at Parenzo (Sixth Century), Sant' Ambrogio, Milan (Ninth Cen tury), San Clemente, Rome (Eleventh and Twelfth centuries), and in the cathedrals of Capua and Salerno are the best preserved. In the monastic architecture of the early and Mid dle Ages, the cloister was evidently the atrium moved from the front to the side of the church, and reserved for the use of the monks. See CLOISTER.