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.

In an ancient Roman house, an open central court that contained the impluvium, a basin where rainwater collected. It originally contained the hearth and functioned as the center of family life. The term later came to be used for the open front courtyard of a Christian basilica, where congregants collected before services. The atrium was revived in the 20th century in the form of glass-covered, greenery-filled multistory spaces sometimes found in shopping centers, office buildings, and large hotels.

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Atrium may refer to:

• Atrium (architecture), a large open space within a building
• Atrium (heart), an anatomical structure of the heart
• Atrium (Cardiff), a University of Glamorgan (Wales) building in Cardiff
• Atrium (band), A screamo band based in York, PA.