The Flavian amphitheater is the third largest arena in the Roman world, after those of Rome and Capua, testimony to the extraordinary technique achieved by ancient engineering. It was located near the intersection of roads from Naples, Capua and Cuma. It has three superimposed orders, four major and twelve secondary entrances and a quarry for about 40,000 spectators. The amphitheater was also the center of urban life: in the galleries under the external ambulatory there were places of worship and the headquarters of many professional associations, known through inscriptions. Suggestive is the visit of the underground that show the complex organization of services for the functioning of the shows. The first Christian martyrs took place in the arena: here, according to the tradition formed between the fifth and sixth centuries, in 305 AD. the punishment for San Gennaro and his companions was prepared at first; the sentence was then executed at the Solfatara. In memory of the presence of the Saint, in 1689 a small church was built in the area, destroyed at the time of the excavations in the nineteenth century and replaced by a small chapel still visible in the ambulatory.
Unique testimony of the port and commercial districts of PUTEOLI is the 'Temple of Serapis', so named because here was found a statue of the Egyptian deity (today at the National Archaeological Museum of Naples). In reality, the structure is one of the major examples of MACELLUM, the market for edibles, erected between the end of the first and the beginning of the 2nd century AD. and restored at the time of the Severi dynasty (3rd century AD). The shops were lined up on the sides of a large porticoed and marble paved courtyard. On the far side there was a room for the imperial cult and the gods of the market (including Serapis). The three columns in cipolin marble belong to the pronaos of this sacellum. These columns, with the bands of small holes dug all around by the lithodomes (marine mollusks digging their burrow in the stone), are the most obvious indicators of the phenomenon of bradyseism. The sumptuous building is decorated with precious marble floors and a characteristic element is the large round (THOLOS) in the middle of the courtyard, embellished with a colonnade of sixteen African marble columns and friezes of marine animals on the base.