Encyclopædia Britannica, Ninth Edition/Atrium
ATRIUM, the principal apartment in a Roman house, was entered through the ostium or janua, which opened off the vestibulum, a clear space between the middle of the house and the street, formed by the projection of the two sides. It was generally quadrangular in shape, and was roofed all over, with the exception of a square opening, called compluvium, towards which the roofs sloped, and by which the rain-water was conducted down, to a basin (impluvium) fixed in the floor. The opening in the roof seems sometimes to have been called impluvium (Terence, Eun., iii. 5 ; Phorm., iv. 4). In the early periods of Roman civilisation, the atrium was the common public apart ment, and was used for the reception of visitors and clients, and for ordinary domestic purposes, as cooking and dining. In it were placed the ancestral pictures, the marriage-couch, the focus, or hearth, and generally a small altar. Here, too, were kept the looms at which the mistress of the house sat and span with her maid-servants. At a somewhat later period, and among the wealthy, separate apartments were built for kitchens and dining-rooms, and the atrium was kept as a general reception room for clients and visitors. It appears sometimes to have been called cavcedium, but the relation of these two is somewhat obscure. According to some authorities, the cavcedium was simply the open space formed when the impluvium was surrounded with pillars to support the roof ; according to others, the cavce dium was really the principal room, to which the atrium served as an antechamber.
Atrium, in Ecclesiastical Antiquities, denotes an open place or court before a church. It consisted of a large area or square plat of ground, surrounded with a portico or cloister, situated between the porch or vestibule and the body of the church. In the centre was placed a fountain, wherein the worshippers washed their hands before enter ing church. In the atrium those who were not suffered to advance farther, and more particularly the first class of penitents, stood to solicit the prayers of the faithful as they went into the church. It was also used as a burying- ground, at first only for distinguished persons, but after wards for all believers.