Roman Peristylium or Peristylum
The peristylium, or peristylum, was borrowed from the Greeks, but despite the way in which the Roman clung to the customs of his ancestors it wasn't long before the peristylum became the more important of the two main sections of the house.
The Roman peristylium was like a spacious court open to the heavens, but girded on all sides by rooms, all these rooms facing it and having doors and latticed windows opening onto it. Such rooms had covered, sheltered porches on the side adjacent to the court. These porches, forming an unbroken colonnade on the four sides, were strictly the peristyle, though the name came to be used of this whole part of the Roman house, including court, colonnade, and surrounding rooms.
The court was far more open to the sun and elements than the atrium ; a great number of exotic and beautiful plants and flowers grew in this spacious courtyard, shielded from the wind by walls.
The peristylium was usually set up as a small formal garden, with neat geometrical flower beds lined with low brick walls. Evidence from Pompeii has even shown us some of the planting of the shrubs and flowers. Fountains and decorative statuary embellished these small Roman gardens; the colonnade furnished cool or sunny promenades, regardless of the time of day or the season of the year. As the Romans enjoyed the open air and the delights of nature, it is understandable that the peristyle soon was made the center of Roman domestic life in the houses of the wealthy classes, and the atrium became restricted to the scene of more formal functions which their political and social status required.
Often there was a garden behind the peristyle, and frequently there was as well a direct connection between the peristyle garden and the street.