The macellum, also known as the temple of Serapis, represents a real unicum of the historical-artistic panorama of the Phlegraean Fields, for its dual archaeological and scientific interest. It is improperly called the temple of Serapis because in 1750, during the first excavation, a statue of the Greek-Egyptian god Serapis was found there, a faithful reproduction of which is preserved in the Archaeological Museum of the Phlegraean Fields. The site, of which only the three marble columns initially emerged, was then brought to light in full with subsequent excavations, dating back to the early nineteenth century. In 1907, the French scholar Charles Dubois attributed the function of a macellum to the building: a food market, built not far from the Roman city emporium, between the end of the 1st and the beginning of the 2nd century. A.D., and restored in the Severan period.

In addition to the inestimable historical value for the territory, the scientific aspect of the macellum is also interesting: the three columns currently visible, having been corroded by marine molluscs that dig the stone called lithodomes, in fact document the variations in the level of the waters that have invaded the fence of the monument. The continuous sinking and resurfacing over the centuries are due to the phenomenon of bradyseism (from the Greek bradýs - slow and seismós - shock): slow vertical movements of the ground imperceptible to man, which have always affected the Phlegraean area.

The site extends into a rectangular area in the center of which there was a courtyard surrounded by a portico of granite columns. Four of these columns, three of which still standing and a fourth overturned on the floor, were distinguished from the others by the different types of marble, cipollino rather than granite, and by their larger dimensions. Their majesty served to constitute the monumental facade to a large semicircular room located at the bottom of the complex. On the long sides of the rectangle there were instead the various shops, the tabernae, with entrances that opened both on the portico and on an ancient street that surrounded the whole complex.

The interior of the courtyard is occupied by a circular building called thòlos: the monumental entrance, the polychrome marble floor, the presence of statues, made the thòlos and the surrounding environment a large and important sanctuary, dedicated to the cult of the protective deities of the fortunes and trade of the city.

The interior of the courtyardisoccupied by a circular building calledthòlos: the monumentalentrance, the polychromemarblefloor, the presence of statues, made the thòlos and the surroundingenvironment a large and importantsanctuary, dedicated to the cult of the protectivedeities of the fortunes and trade of the city.