The atrium was the heart of the ancient Roman house. The most notable features of the Roman atrium were the compluvium and the impluvium. The water collected in the impluvium was carried into cisterns; across the compluvium a curtain could be drawn when the light was too intense, like across a photographer's skylight today. The two words were carelessly used interchangeably by Roman writers. So important was the compluvium to the atrium that the atrium was named from the way in which the compluvium was constructed.
Types of Roman Atriums
We learn from Vitruvius that there were four styles of ancient atriums. The first was called the atrium Tuscanicum. In this one the roof was formed by two pairs of beams crossing each other at right angles; the enclosed space was left uncovered and thus formed the compluvium. It is clear that this method of construction could not be used for rooms of large size. The second style of atria was called atrium tetrastylon. The beams were supported at their intersections by pillars or columns. The third, atrium Corinthium, differed from the second only in having more than four supporting pillars. The fourth was called the atrium displuviatum. In this the roof sloped towards the outer walls, and the water was carried off by gutters on the outside; the impluvium collected only so much water as actually fell into it from the heavens. We believe that there was another style of atrium, the testudinatum, which was covered all over and had neither impluvium nor compluvium.
Changes in the Roman Atrium
In the very early years of the Roman republic the atrium was a fairly simple family area where most of life was lived but by Cicero's time the atrium had ceased to be the center of domestic life; it had become a state apartment used only for display. We don't know the exact steps in the process of change. Probably the rooms along the sides of the atrium were first used as bedrooms, for the sake of more privacy. The need for a detached room for the cooking, and then of a dining room, was felt as soon as the peristylium came into use. Then other rooms were added around the peristylium, and these were made bedrooms for the sake of even more privacy. In the end these rooms were needed for other purposes and the sleeping rooms were moved again, this time to an upper story. When this second story was added we don't know, but it presupposes the small and costly lots of a city. Even simple houses in Pompeii have the remains of staircases.
The atrium was now fitted up with all the splendor and magnificence that the house owner's wealth would allow. The opening in the roof was made larger to let in more light, and the supporting pillars were made of marble or expensive wood. Between these pillars, and along the walls, statues and other works of Roman art were placed.
Compluvium in a Tuscan Atrium.
The impluvium evolved into a marble basin, with a water fountain in the middle, and was often elaborately carved or adorned with figures in relief. The floors were mosaic, the walls painted in brilliant colors or paneled with marbles of many hues, and the ceilings were covered with ivory and gold. In such an atrium the host greeted his guests, the patron, in the days of the Empire, received his clients, the husband welcomed his wife, and here the master's body lay in state when he died.
Persistence of Older Traditions
Still, some memorials of the older day were left in even the most imposing atrium. The altar to the "Lares" and "Penates" sometimes remained near the place where the hearth had been, though the regular sacrifices were made in a special chapel in the peristylium. In even the grandest houses the implements for spinning were kept in the place where the matron had once sat among her slave women, as Livy tells us in the story of Lucretia. The cabinets retained the masks of simpler and, perhaps, stronger men, and the marriage couch stood opposite the ostium (hence its other name, lectus adversus), where it had been placed on the wedding night, though no one slept in the atrium. In the country much of the old time use of the atrium survived even in the days of Augustus, and the poor, of course, had never changed their style of living. What use was made of the small rooms along the sides of the atrium, after they had stopped being used as bedchambers, we don't know; they served, perhaps, as conversation rooms, private parlors, and drawing rooms.