Atrium
The atrium (plural: atria) was a central room in a Roman house with an open air skylight in the ceiling. It is likely derived from the Greek aithrion (αἴθριον), meaning opened to the sky, in reference to the part of the atrium open to the sky. The name of this room lends itself to a particular type of Mediterranean house style, the atrium-style house, in which the residence is centered around the atrium. A house could have more than one of these rooms, but typically the main atrium was located just inside the entrance to the house, between the entry and the tablinum. Other rooms may also be situated around the sides of the atrium. The atrium performed a number of important functions in the Roman house. It was a source of both light and ventilation. Roman houses, particularly in urban environments, did not typically have many exterior windows, and so open air features of interior spaces became important sources of light and ventilation.
The atrium was also important for the collection of rainwater. Many atria were fitted with two structures, the compluvium and impluvium. The roof around the room would typically be angled inward toward the opening, allowing for the funneling of rainwater on the roof toward this opening. This angle would either funnel the rain water directly down through the opening, or would collect it in a series of rain gutters lining the interior of the open space. This entire roof structure of the atrium was called the compluvium (plural: compluvia), from the Latin cum and pluit, with the rain. This collected water was then funneled down or directed down into a structure below the compluvium called the impluvium (plural: impluvia), from the Latin impluit, to rain upon. The area directly under the open space would be a collection basin for the rain the fell through or was directed into the opening. If the rain was funneled via rain gutters, a pipe would bring the water down into this area. The water would then be drained into a cistern beneath the impluvium for later use. The evaporation of water from the cistern combined with the air circulation coming in from the skylight would also serve as a sort of evaporative cooling mechanism for the house.
There were several different types of atria based on the details of the design. While they all mostly functioned the same way, some styles would have been decorated with columns. The atrium, often being the first main room inside the house from the entrance, would also serve as a reception area, and so like other rooms of the house used for hosting guests (such as the tablinum or triclinium) would have been richly decorated so as to project the wealth and taste of the owner.
