The object that dominates the center of the room is a sundial. It is made from a single block of marble, within which a dial in the shape of a truncated cone has been carved. The surface is engraved with three concentric arcs and eleven radial lines, dividing the dial into twelve hourly sectors. The widened base of the block ensured the stability of the object. At the top of the dial, the hollow where the gnomon was fixed is still visible—a slender bronze rod that stood above the cone and whose projected shadow indicated the hour.
The sundial was the most commonly used instrument for measuring time using the sun, dividing each day into twelve hours from sunrise to sunset (and an equal number of hours for the night). Various models have been found during excavations of domus and villas in Campania. All types are described by Vitruvius in his treatise De Architectura, in which he attributes their invention to Greek or Chaldean scholars who lived between the 4th and 3rd centuries BC. These instruments quickly spread throughout the Roman world, becoming widespread as early as the 1st century BC.
Such objects adorned public squares and could also be found near baths, temples, forums, or in the gardens of grand private residences. This particular example comes from the House of the Mosaic Atrium, a sumptuous residence overlooking the beach. Made of marble, it was a luxury item. More than just a functional tool, it served to embellish the garden—a green and joyful setting for spring and summer banquets.