Underground Rome, more unusual and unknown, is able to offer the visitor continuous surprises and emotions which are difficult to find elsewhere. It is a buried city, made of hypogea, columbaria and Mithraea, but also of buildings made to be illuminated by sunlight and then ending up buried by the stratification of the soil with the slow passing of time.
Our itinerary starts with the Basilica of San Clemente, situated only three hundred metres from the Colosseum, facing onto the square of the same name and also reachable from Via di San Giovanni in Laterano. The visit to the church's underground levels enables us, going down level by level, to go thousands of years back in time. The base of the building corresponds, in fact, to a 2nd-century house, in the Courtyard of which was later created a Mithraeum, a grotto-shaped room, devoted to the worship of the Persian god Mithras. Along the walls are arranged the stone benches with which the faithful celebrated the sacred banquet. In the centre of the room is still visible the altar with the cult's image: the god killing the bull, a symbol of good and fertility.
Mithraism, which was widespread in 3rd-century Rome, was a mystery religion with a ritual similar in some ways to that of Christianity. The worshippers had to go through an initiation procedure through seven levels, and their "baptism” took place with the blood of the bull sacrificed to the god. A decisive moment of the rite was the banquet based on bread, wine and water, which the initiates took together in the grotto.
In the 4th century a church rose over the Mithraeum; it was abandoned after seven centuries because it was unsafe, and rebuilt on the upper level, that of the current basilica.
In the lower church it is worthwhile to dwell a moment on the fresco of the central nave, which represents the Story of Sisinius. The inscription under it constitutes an extremely important document for the study of the first expressions of the Italian vernacular.
From San Clemente we can take Via Labicana to go towards the park of the Oppian Hill. Almost at the park entrance is the access to Nero's famous Domus Aurea (Golden House). The huge underground rooms, in some cases still adorned with splendid paintings, manage to communicate only a tiny part of what must have been the magnificence and monumentality of the complex that the emperor Nero had built, on an area of 80 hectares, after the disastrous fire of 64 A.D. caused, according to legend, by the emperor himself.
In the early 2nd century, the emperor Trajan used what remained of the Domus Aurea as the foundations for his Baths, transforming the splendid reception halls into the present-day dark underground rooms. During the Renaissance, the greatest artists all went down into these rooms and, fascinated, imitated the motifs they found frescoed on the vaults, giving rise to the painting style called ”grotesque”.
The term grotesque derives from the Domus Aurea and its state when it was discovered in the late 14005. Buried, and thus hidden like a grotto, in order to visit it, it was necessary to climb in from above, after opening holes which are still visible in the ceilings of the rooms. The frescoes found inside were thus called grottesche, an expression still used today to indicate all the paintings which derive stylistically from the Domus Aurea.
Ancient authors write of the Domus Aurea: “Everything was gilded and adorned with gems and mother-of-pearl; the banquet halls with revolving ivory panels, to allow flowers to be sprinkled from above, and equipped with conduits to pipe in perfumes; the main banquet hall was round and turned continuously, day and night, like the universe”.
Taking Via dei Fori Imperiali, we can reach the church of San Giuseppe dei Falegnami, in the basement of which it is possible to visit the Mamertine Prison (named after the Sabine god Mamers, corresponding to the Latin ”Mars”). The building is on two levels: the upper part, trapezoidal in shape, is the actual Mamertine Prison, known with this name since the Middle Ages; the lower part, instead, is the Tullianum, a cavity so called already in Roman times due to the presence of a spring, or perhaps a cistern (in Latin tullus). The lower room, dark, damp, and constantly covered with a layer of water, was used to hold political prisoners awaiting execution. Here the death sentences were carried out by strangling, involving individuals such as Jugurtha, king of Numidia, and Vercingetorix, chief of the Gauls, overcome by Julius Caesar in 49 B.C.
According to a legend that spread during the Middle Ages, the Apostles Peter and Paul were allegedly ímprísoned here for nine months, escaping after having converted their guards. Furthermore, St. Peter was said to have made a spring of water gush miraculously from the stones of this prison.
The itinerary continues towards Piazza Venezia, Via del Plebiscito and Corso Vittorio Emanuele II. On reaching the Church of Sant'Andrea della Valle, we turn right onto Via dei Chiavari, and proceed until reaching Piazza di Grotta Pinta. Worthy of note is the particular shape of this piazza, which outlines a semicircle with the surrounding buildings. This original shape reflects the internal curve of the Theatre of Pompey, and constitutes one of the most remarkable cases of Roman urbanistic continuity. The theatre, completed with a huge colonnade, was the first to be built of masonry in Rome, between 61 and 55 B.C., and extended over a vast area stretching between Largo Argentina and Campo de' Fiori.
In the underground parts of the archaeological area of Largo Argentina it is still possible to see the large exedra that opened up along the colonnade. During the time of Pompey, the Senate met here, and it was here that Julius Caesar was killed on 15 March 44 B.C.
After returning to Corso Vittorio Emanuele ll we can go towards the Museo Barracco on Via dei Baullari, set up inside the 16th-century Palazzetto Le Roy, also known as the Piccola Farnesina (referring to the fleurs-de-lis on the façade, taken for the Farnese lilies). With permission requested from the caretakers, we can go down into the museum basements where, 4 metres beneath the current street level, there are interesting structures pertaining to a construction dating from the mid-4th century, probably a rich man's house. It is possible to see the remains of the colonnaded Courtyard with its splendid pavement of polychrome marble slabs, the capitals of columns and a circular marble basin. Later masonry work and the presence of a weighing table (a block of marble into which hollows used as sample measures for grain, flour, etc. were carved) seems to indicate a reuse of the building for trade purposes.
Near the Museo Barracco is the Palazzo della Cancelleria that incorporates into its ground floor the Basilica of San Lorenzo in Damaso. In the basement of the palace is the tomb of Aulus lrtius, a consul who died, together with his colleague Gaius Vibius Pansa, in 43 B.C. during the battle of Modena against Mark Antony. It is a square enclosure in brick on a peperino base with various cippi at the corners on which is engraved the funeral inscription. Also running through here is a stretch of the Euripus, a channel of the 1st century B.C. that connected the Tiber to the artificial lake near the demolished Baths of Agrippa, which stood in the zone of Torre Argentina. The tomb and the channel can be seen today at a depth of 8 metres underground, but they were originally at ground level and in the open air, in an almost idyllic setting, rich with orderly vegetation