Pozzuoli is the most important place in the Campi Flegrei. Along the beautiful panoramic road is the Church of San Gennaro, where the stone, popularly believed to be the blood-stained stump of the Saint, is preserved. The stain takes on the vivid colouring of the blood when in the Cathedral of Naples the blood changes into liquid form. In front, a footpath goes to the access to the Solfatara Crater, a spectacular volcano that began erupting 4000 years ago. Today, continuous gas emissions containing water vapour, sulphur and sulphides create an evocative and almost surreal scene. After 3 km, you get to the Amphitheatre, the third largest after the Coliseum in Rome and the one in Santa Maria Capua Vetere, in Capua.
From here, if you continue in the direction of Corso Terraciano, you will come across the ruins of the so-called Temple of Neptune, a thermal building from the 1st century, and those of the Nymphaeum of Diana (of which the circular base and part of the elevation are preserved). If, on the other hand, you take Via Carlo Maria Rosini, you arrive at the old city of Pozzuoli. The road crosses a splendid landscape and passes the entrance to Rione Terra, one of the best-preserved historical centres in Campania, which developed on the area of the primitive Roman colony, the heart of ancient Puteoli, the Roman Pozzuoli.
The district was evacuated in the 1970s following repeated earthquakes caused by bradyseism, the volcanic phenomenon specific to the Campli Flegrei, which manifests itself with traumatic uplifts and subsidence of the ground. Inaccessible for over twenty years, Rione Terra has been rescued and transformed into a area of art and culture that can be visited since 2005. The consolidation work uncovered an important archaeological site, now partly open to the public, which shows, through a suggestive itinerary, the Greek-Roman city and the seventeenth-century urban layout. There was here the glorious Puteolan acropolis stood, ending in the Temple of Augustus, the remains of which were incorporated in the 17th century in the construction of the Cathedral of St. Proculus. Excavations have uncovered the decumanus major, from the first Roman settlement, some public buildings, baths and tabernae used for catering, and a pistrinum: a bakery with several rooms for grinding wheat and making bread.
Along Via Campana, in the direction of Quarto, in the nearby San Vito necropolis you can see a tomb of bricks with a square base and a cylindrical drum with external architectural decoration.
Also worth mentioning are the Baths of Neptune that took up several terraces towards the sea, although almost nothing remains today, and the remains of the Nymphaeum of Diana, a circular room within a rectangle that was probably connected centuries ago with the lower baths.
In Pozzuoli, the Romans built the most important port of the Roman Empire, visible in its totality from the Cristoforo Colombo seafront, which is one of the best examples of ancient port engineering (it rested on 15 pillars joined by arches). Next to the trading port is the macellum, the public market of Putèolis. These ruins were long considered first the remains of the Temple of Serapis, due to the discovery of a statue of the Egyptian god, and later a thermal building.
Only in the last century was its real function discovered. Built between the end of the 1st and the beginning of the 2nd century, it consisted of shops arranged around a large colonnaded courtyard with a marble floor, accessible from both the square and the perimeter streets. The majestic building was a victim of bradyseism in the area: on its columns are evident the holes dug in the stone by sea molluscs when the phenomenon caused the structure to sink, then appear again.