A widely published series of sestertii of Nero from AD 64 (RIC I 178, 181; BMC 134) from the mint in Rome with the harbor at Ostia on the reverse is commonly associated with the completion of the harbor, Portus Augusti, begun by Claudius and, allegedly, completed by Nero. Most scholars conclude that the coin was struck on the occasion of the completion of the harbor by Nero. I conclude, however, that the coin presents no direct claim about completing the harbor works at Portus. The images of the harbor, its monuments, buildings and facilities that surround the field on the coin’s reverse differ throughout the series in a number of basic ways suggesting that it is not intended to document a specific building program. Furthermore this conclusion that Nero completed the harbor is not supported by references in any literary or documentary sources. If instead we examine the context for the coins and the consistent elements of imagery on them, it seems clear that they served a different, very specific purpose: to reassure people in Rome about the safety and security of the grain supply in the period following the disasters of AD 62.
Tacitus (Annals 15.18) records the food insecurity of 62 when two hundred ships of the grain fleet were destroyed by a storm in the harbor at Ostia and an additional one hundred were destroyed on the Tiber by an accidental fire, a loss of 10-15% of the grain fleet. In the same passage Tacitus relates Nero’s attempts to reassure the Roman populace about the security of the food supply suggesting that these events led to widespread anxiety that required an imperial response. The ships within the harbor basin on the coin reverses are of three types, with most variations showing one harbor boat, a galley and a larger but variable number of merchant ships. Details of the merchant ships, notably the use of top sails, conform to the grain fleet, which as Seneca reports from his eyewitness account (letter 77), were the only ships allowed to use that sail in harbor. The galley is a specialized vessel type known to have accompanied the grain fleet forprotection.
The context for the fleet in the harbor is provided by the figures visible on some of the ships and on the edge of the harbor standing before an altar. All are performing the arrival sacrifice, thanksgiving for safe passage into the harbor. This specific sacrifice is known from an account of Alexandrians who made it on their arrival into the important harbor of Puteoliunder Augustus (Suet. Aug. 93). It is also depicted on the Severan period Torlonia relief found at the harbor of Portus on which another captain makes an identical sacrifice at an altar on board a merchant ship in the harbor basin.
I conclude that the message of the coin is not to commemorate the completion of harbor works under Nero, but to celebrate the arrival of the grain fleet and therefore the security of food supply for Rome following the disasters of AD 62. This security had long been the personal responsibility of the emperor (Tacitus Ann. 3.54; Suet.Claud. 18.2) and Nero’s coins are apparently one component of his program to declare that he is fulfilling that responsibility with the successful arrival of the grain fleet and the return of food security to Rome. Struck in Rome these coins were probably designed to circulate there among those most directly affected by a grain shortage. Its denomination would ensure wider circulation than a gold or silver coin and that it would be seen by more of the approximately 30% of the city that relied on the grain dole under Nero.