The arrangement of the houses, though varied, of course, by local circumstances, and according to the rank and circumstances of the master, was pretty generally the same in all. The principal rooms, differing only in size and ornament, recur everywhere; those supplemental ones, which were invented only for convenience or luxury, vary according to the tastes and circumstances of the master.
[Illustration: GROUND PLAN OF A ROMAN HOUSE.]
The private part comprised the peristyle, bed-chambers, triclinium, oeci, picture-gallery, library, baths, exedra, xystus, etc. We proceed to explain the meaning of these terms.
Before great mansions there was generally a court or area, upon which the portico opened, either surrounding three sides of the area, or merely running along the front of the house. In smaller houses the portico ranged even with the street. Within the portico, or if there was no portico, opening directly to the street, was the vestibule, consisting of one or more spacious apartments. It was considered to be without the house, and was always open for the reception of those who came to wait there until the doors should be opened. The prothyrum, in Greek architecture, was the same as the vestibule. In Roman architecture, it was a passage-room, between the outer or house-door which opened to the vestibule, and an inner door which closed the entrance of the atrium. In the vestibule, or in an apartment opening upon it, the porter, _ostiarius_, usually had his seat.
The atrium, or cavædium, for they appear to have signified the same thing, was the most important, and usually the most splendid apartment of the house. Here the owner received his crowd of morning visitors, who were not admitted to the inner apartments. The term is thus explained by Varro: "The hollow of the house (cavum ædium) is a covered place within the walls, left open to the common use of all. It is called Tuscan, from the Tuscans, after the Romans began to imitate their cavædium. The word atrium is derived from the Atriates, a people of Tuscany, from whom the pattern of it was taken." Originally, then, the atrium was the common room of resort for the whole family, the place of their domestic occupations; and such it probably continued in the humbler ranks of life. A general description of it may easily be given. It was a large apartment, roofed over, but with an opening in the centre, called _compluvium_, towards which the roof sloped, so as to throw the rain-water into a cistern in the floor called _impluvium_.