Between the basins of Claudius and Trajan is an interior mole, known prosaically as the North-south mole. Today it is completely landlocked, but visible as a ridge in the terrain. In the past it has been attributed to the fourth century, and regarded as extra protection for Trajan's harbour. Reused parts of marble columns were seen, that had been inserted vertically in the mole and could be used for mooring.
Near the mole, marble columns were found with the inscriptions DNGF, FLST and FLSTLC. The shape of the letters points to a date in late antiquity. FLST has been explained as FL(avi) ST(iliconis), "of Flavius Stilicho", the famous general from the late fourth and early fifth century (similar objects were found on the Mole of the Small Lighthouse). In 1907 Jérôme Carcopino found a marble block (1.68 x 0.45 x 0.45) with the text AVGVRINCOS; an Augurinus was consul in 132 and 156 AD.
Marble column with the inscription FLSTLC. CIL XIV, 165.
Rome, Palazzo Cesarini-Sforza. Photo: Pensabene 1994, fig. 222.
Some cleaning took place in 1991, followed by a short report. In recent years excavations were carried out by the École française de Rome, led by Évelyne Bukowiecki. The excavators had to cope with anti-Covid 19 measures and with the find of ammunition for rifles, remains of an observation post from the Second World War. Trenches were dug at the south end near a small modern utilitarian structure, and at the north end near an old agricultural building known as Casaletto, which stands on top of the mole. It would make sense if there had been a beacon or even a small lighthouse here in antiquity.
Aerial view with the locations of the trenches dug by the École française de Rome. Photo: Bukowiecki et al. 2021, fig. 1.
Remains of the mole. Photo: Parco Archeologico di Ostia Antica.
The date of the original mole is not certain. It may have been built when the harbour of Claudius was constructed, to separate the basin from the area to the east with the Inner harbour. It was some 14 meters wide. It was reinforced and extended towards the north twice, in the Severan period and in late antiquity, dates deduced from brickwork. It was thus brought to its final length of approximately 300 meters, with new sections that were seven to eight meters wide.
Suggested construction phases of the mole: period of Claudius; Severan period; late antiquity.
Image: Bukowiecki et al. 2019, fig. 1.
Late-antique masonry (USM 17) set against Severan masonry (USM 14). Photo: Bukowiecki et al. 2021, fig. 4.
Later, in the early Middle Ages it seems, an opening was created in the south part of the mole, so that ships could reach the basin of Trajan without circumnavigating the mole. This may have been necessitated by the silting up of the basin of Claudius. The opening is also depicted on the reconstructions from the 16th century.
The mole in the reconstrucion by Georg Braun and Frans Hogenberg from 1580.
At the south end of the mole, where it started, rooms belonging to baths were found. These are mentioned already by Giuseppe Lugli in 1935. After the recent excavations by the École française de Rome they were called Baths of the Traveller (Terme del Viaggiatore). Part of the heated area of the baths was investigated: a room was unearthed with a raised floor and heating pipes set against the wall. To the south is a semircircular basin, to the east a square one. To the south of the latter basin are the remains of a round furnace with a diameter of 1.20 m. Floors and walls were decorated with white marble.
Plan of the baths. Photo: Bukowiecki et al. 2022, fig. 14.
The baths can be dated to c. 350 AD through the find of coins from the first decades of the fourth century. They stopped functioning when the late-antique city wall was built, here assigned to the last quarter of the fifth century.
View of the baths from the south. Photo: Bukowiecki et al. 2022, fig. 3.
View of the baths from the west. Photo: Parco Archeologico di Ostia Antica.
Below the baths a drainage system was found made of amphoras from the years 30-40 AD. It might be related to the first phase of the mole.
The drainage system of amphoras. Photo: Bukowiecki et al. 2022, fig. 5.
Sources
See in the online bibliography the topic "Portus - Buildings - Molo nord-sud" and: Carcopino 1907 (NSc), 737-738; Calza 1925, 70; Lugli-Filibeck 1935, 78-81; Pensabene 1994, 170-173, 181, 188, 192; Verduchi 2004 (non vidi).