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The harbour of Claudius

The river harbour of Ostia had several limitations. Large ships could not enter it, because there was a sand bar in front of the mouth. Therefore goods that arrived in large ships had to be transferred to smaller ships on the sea. Shallow-draught vessels could moor at the Tiber quays, but here there was not enough capacity for Rome's growing needs.

In 42 AD Claudius started the construction of an artificial harbour, a few kilometres to the north of Ostia. There may have been a small, natural bay here. A huge basin was created, partly dug out, protected by two curved moles and with a lighthouse. Recent research suggests that there was a long and uninterrupted northern mole. The southern mole may have been shorter. A number of ships filled with concrete was used as foundation. The width of the basin was c. 800 metres, the depth a few kilometres. It was seven metres deep.

Two channels connected the Tiber with the sea. One is to the north of Portus. It was meant for flood relief, and 20-35 metres wide. The other channel is to the south of the city and 45 metres wide. It is known as the Fossa Traiani or Traiana, but it was made by Claudius. This channel was in the Middle Ages called Fiumicino ("Small river"), as was the modern village at the mouth of the channel (the river leading to Ostia was called Fiumara Grande). To the south of the basin was a small inner harbour. A short transverse channel, running from north to south, connected it with the Fossa. The Fossa created an artificial island between Ostia and Portus, called Isola Sacra ("Sacred Island") in late antiquity, and earlier also Assis.

Capo Due Rami, where the Fossa Traiana (to the right) branches off from the Tiber.
Photograph: Antonia Arnoldus-Huyzendveld.

The work of Claudius is mentioned in an inscription from 46 AD, possibly from the attic of an arch (Thylander B310), which shows that Claudius also hoped to reduce the risk of inundations in Rome, by digging channels from the Tiber to the sea:

TRIB(unicia) POTEST(ate) VI CO(n)S(ul) DESIGN(atus) IIII IMP(erator) XII P(ater) P(atriae)

Coins seem to celebrate the completion of the work in 64 AD, during the reign of Nero. But already in 62 AD the harbour was in use: in that year 200 ships in the basin perished during a storm. This may have been a tsunami, the result of the same seismic activity that is documented in that year in Pompeii (the earthquake of February 5, 62 AD). The coins may however also be related to the celebration of the 10th anniversary of the completion of the harbour. On these coins the two moles are not identical. The one on the right has arches. On some coins of the series there seem to be a temple and an altar at the end of the left mole. The lighthouse is not depicted between the moles, but only a statue of an Emperor that was on top of it. A reclining male figure with rudder and dolphin is probably the personification of the harbour.

Portus on a coin of Nero

Portus on a sesterce issued by Nero, in 64 AD.
Legend: AVGVSTI | S POR OST C = Portus Ostiensis Augusti, senatus consulto.
© Classical Numismatic Group. Reproduced with permission.

The harbour was called Portus Augusti Ostiensis or Portus Ostiensis. Behind the harbour were commercial buildings, but also a residential area, witness the find of tombs. From the harbour the goods were taken to Rome in barges that were towed by oxen.

[jthb - 30-Mar-2008]