A giant cargo ship
A harbour for Rome should be able to accommodate very large ships. In 37 AD Caligula transported an obelisk from Alexandria to Rome, via Ostia and the Tiber. It was to be erected on the spina of the Vatican Circus. Pliny the Elder mentions the admiration for the cargo ship that was used for the transport, in his discussion of the transport of obelisks to Rome:
As to the ship in which, by order of the Emperor Caius, the other obelisk had been transported to Rome, after having been preserved for some years and looked upon as the most wonderful construction ever beheld upon the seas, it was brought to Ostia, by order of the late Emperor Claudius; and towers of Puteolan earth being first erected upon it, it was sunk for the construction of the harbour which he was making there. And then, besides, there was the necessity of constructing other vessels to carry these obelisks up the Tiber; by which it became practically ascertained, that the depth of water in that river is not less than that of the river Nile.
The obelisk transported by Caligula, now on Saint Peter's square.
Photo: Wikimedia, Jean-Pol Grandmont.Pliny also describes the enormous size of the main mast of the ship:
An especially wonderful fir was seen on the ship which brought from Egypt, at the order of the Emperor Gaius, the obelisk erected in the Vatican Circus and four shafts of the same stone to serve as its base. It is certain that nothing more wonderful than this ship has ever been seen on the sea. It carried 120,000 modii of lentils for ballast, and its length took up a large part of the left side of the harbour of Ostia, for under the Emperor Claudius it was sunk there with three moles as high as towers erected upon it, that had been made of Puteoli earth for the purpose, and conveyed to the place. It took four men to span the girth of this tree with their arms. And we not unfrequently hear of the price of masts for such purposes as being eighty thousand sesterces or more; rafts, too, of this wood are sometimes put together, the value of which is forty thousand.
The largest containership in the world, entering the port of Rotterdam.
Photo: Port of Rotterdam, Ries van Wendel de Joode.This then brings us to Claudius's decision to build an artificial harbour to the north of Ostia. But could it be done? Quintilianus, looking back at the end of the second century, describes the uncertainties in his book about the education of the orator:
As for a proposal, its practicability is either certain or doubtful. If it is doubtful, this becomes the only or at least the most vital question. We shall often find ourselves saying first that a thing ought not to be done even if it could, and secondly that it cannot be done. When the question turns on this, we have conjecture: can the Isthmus be cut through, can the Pontine Marsh be drained, can a harbour be made at Ostia, will Alexander discover lands beyond the Ocean? When the construction of the harbour at Ostia was discussed, was it not an orator's duty to state his view? Yet it needed the technical knowledge of the architect.
