atrium, term for an interior court in Roman domestic architecture and also for a type of entrance court in early Christian churches. The Roman atrium was an unroofed or partially roofed area with rooms opening from it. In early times its center held a cooking hearth. After the 2d cent. B.C., when the hearth was placed elsewhere, the center of the atrium held a tank (impluvium) to receive rainwater falling through the opening, which also furnished light to the surrounding rooms. In more luxurious and complex Roman dwellings, the private apartments had a court of their own, called the peristyle, and the atrium served merely as a semipublic reception hall. The ruins of Pompeii contain remains of atria in their various forms. In early Christian churches, the atrium was a large arcaded or colonnaded open court, serving as a general meeting place, in front of the church itself, with a fountain used for ablutions in its center. The basilican churches of Sant'Ambrogio in Milan and San Clemente in Rome have noteworthy atria. This type of large forecourt is also a characteristic element of the Muslim mosque. The term also refers to a modern building's central court, an often soaring interior space with a large skylight. Creating a flood of natural light and usually filled with plants, the feature has become practically ubiquitous in contemporary architecture; it is used predominantly in commercial buildings.