Impluvium

The impluvium is the sunken part of the atrium in a Greek or Roman house (domus). Designed to carry away the rainwater coming through the compluvium of the roof, it is usually made of marble and placed about 30 cm below the floor of the atrium.

Inspection (without excavation) of impluvia in Paestum, Pompei and Rome by an American Civil Engineer indicated that the pavement surface in the impluvia were porous or the non-porous stone tiles were separated by a gap significant enough to allow a substantial quantity of water to stand in the basin of the impluvium, filter through the cracks and through layers of gravel and sand into a holding chamber below ground.