Macellum of Naples

What is there today

The excavation lies under the Gothic church and its cloister, where Neapolis had its forum, the successor of the Greek agora (Scabec; en.wikipedia). The market itself was a rectangular porticoed building with shops round an open courtyard paved with mosaics; at its centre stood a small round building, a tholos, which en.wikipedia and Scabec describe as a food stall and it.wikipedia, citing the remains of a drain, as a fountain house. The porticoes ran along the sides of today’s cloister (it.wikipedia).

The lower levels hold the more striking remains. A paved street, identified as the cardo of Neapolis and about 60 m long, runs beneath the church’s transept, following the line of today’s Vico Giganti (Scabec; it.wikipedia). Along it a Roman building in three wings, which also held up the market terrace above, opens onto the street in nine shops of two barrel-vaulted rooms each, with an oven and tanks for dyeing cloth among them. At the end of the passage is the cryptoporticus, a covered market hall divided into small rooms with masonry counters, three of which are thought to have been the city treasury, the aerarium (Scabec). Part of the mosaic floor of a 6th-century early Christian basilica can be seen under the transept of the church (it.wikipedia), and the museum in the floors above the cloister tells the story of the area from classical archaeology onwards (en.wikipedia).

Three other Roman monuments stand within about 250 m:

• Temple of the Dioscuri. On Piazza San Gaetano, 150 m away, two Corinthian columns of the temple of Castor and Pollux front the basilica of San Paolo Maggiore. The temple was rebuilt in the early imperial period, probably under Tiberius, on foundations attributed to the 5th century BC, and the church took it over in the 8th or 9th century, keeping its façade. The earthquakes of 1686–1688 left four of its eight columns standing, and two more were removed in the early 18th century (it.wikipedia).
• Roman theatre. About 200 m to the north-west, in the blocks between Via Anticaglia, Via San Paolo and Vico Giganti, lies the theatre where Nero made his singing debut. Its seating held 5,000 to 6,000 people and some rows still carry their marble facing. Houses were built over it from the 15th to the 17th century, and two massive arches that once braced its outer wall are now part of the houses on Via Anticaglia, where anyone can see them from the street. Inside, one part is reached through a trapdoor in a ground-floor room on Vico Cinquesanti, where the owner of the room had hidden it under a bed that slid aside on rails; the seating in a courtyard off Via San Paolo opens only on special occasions (it.wikipedia).
• Santa Restituta and the baptistery. About 250 m to the north-east, inside the cathedral, Santa Restituta is the oldest basilica in Naples and was its first cathedral; tradition credits Constantine with its founding in the 4th century, and it probably stands on the site of a temple of Apollo (it.wikipedia; Pleiades). Cut down to a side chapel when the Angevin cathedral was built in the 13th century, it keeps 27 ancient columns with Corinthian capitals (it.wikipedia). Off it opens the baptistery of San Giovanni in Fonte, founded by Bishop Severus between the end of the 4th and the start of the 5th century, with the baptismal pool in its floor and mosaics in its dome showing scenes such as the Wedding at Cana, the Samaritan woman at the well and Christ handing over the law (the operator), probably of the 5th–6th century (Sussex database). Beneath the cathedral and Santa Restituta, excavations have exposed a Greek wall, the peristyle of a late imperial house, a stretch of Roman aqueduct and a Greek street (en.wikipedia); the operator’s visiting page does not say whether these are part of the free visit.

Wikidata and Vici.org also list an amphitheatre of Neapolis beside the theatre, but Vici.org marks it as invisible and neither describes anything, so there is nothing to look for.