The origins of Rome’s imperial fleets were in many respects similar to those of the legions and auxilia. In the final bout of civil wars, Octavian’s struggle against Sextus Pompeius and the sea-battle at Actium in 31 bc had highlighted the political importance of controlling the seaways of the Mediterranean, and especially the waters around Italy. At the same time, Octavian had been left with some 700 ships on his hands after the final victory. Much of Antony’s fleet was simply burned, but the rest of the ships were sent with their crews to Fréjus (Forum Iulii) on the southern coast of Gaul (Tac. Ann. 4.5), where a squadron was maintained until the reign of Nero. The main Roman fleets, however, were stationed at Misenum in the bay of Naples, in part to protect the grain transports from Egypt, and at Ravenna at the head of the Adriatic.
These bases were most probably chosen for their large, safe harbours, rather than for strategic reasons, but there were also detachments of the classis Misenatium along the west coast of Italy at Ostia, Puteoli and Centumcellae. The Mediterranean was a Roman lake, known as mare nostrum or ‘our sea’, and the main threat was from civil strife or piracy rather than any external enemy. What mattered was for the emperor to maintain ‘fleets in being’, which could be used if they were needed. In the event they were not required for any major conflict until the civil wars of the early fourth century, and the fleet was mainly used for transport of the imperial family and of troops going on campaign. It is significant that a large detachment of the sailors from Misenum could be kept in Rome to stage mock seabattles (Tac. Ann. 12.56; Suet. Claud. 12.6) and work the sun-awnings in the Colosseum (SHA Comm. 15.6). The sailors of the Italian and other fleets were normally, like the auxiliaries, non-Roman citizens. They even included ex-slaves and Egyptians, who were barred from serving in most other branches of the armed forces. Inscriptions show that the men of the classis Misenatium were recruited mostly from the eastern provinces, especially Egypt, while those of the classis Ravennatium came mostly from the Danube provinces.
A number of provincial fleets were also maintained. One, the classis Alexandrina, was based at Alexandria from the time of Augustus, and was probably a legacy of the war against Antony and Cleopatra. It too was manned by Egyptians, but only those with Alexandrian and Roman citizenship, even though ordinary Egyptians could and did join the Italian fleets. The role of the classis Alexandrina was probably to protect the mouth of the Nile from which the grain ships set sail for Rome, although it also operated on the river Nile from time to time. A Syrian fleet, the classis Syriaca, was probably based at Seleucia at the mouth of the Orontes from some time in the first century ad to protect the coastline of Syria and Judaea. After ad 44 the Alexandrine and Syrian fleets also sent a detachment to Caesarea (Cherchel), the capital of Mauretania Caesariensis in the western Mediterranean.
The other provincial fleets were all based on the northern frontiers and had their origins at the end of the first century bc and in the early first century ad. Several of them were riverine rather than sea-going, including the classis Germanica on the Rhine, with its main base at Cologne, the classis Pannonica on the middle Danube, with its main base near Belgrade (Singidunum) and the classis Moesiaca on the lowerDanube, possibly based around the Danube delta. The duties of such fleets were mainly ferrying and supply, although they did on occasion engage in hostilities on the river. In the Black Sea itself the navy of the kings of Pontus was reorganized as the classis Pontica based on the northern coast of AsiaMinor and in the Crimea. In addition, a British fleet, the classis Britannica, was established when the province was invaded in ad 43, and had its main bases at Boulogne and Dover. Its role, too, was mainly one of transport and supply.
The main capital ship of all the fleets was the trireme, a ship rowed at three levels with a crew of around 200, although the riverine fleets consisted mostly of much smaller biremes and single-level ships. The two main fleets had a few quadriremes (a two-level ship with two men to each oar) and quinqueremes (three-level with one or two men to an oar), and the Misenum fleet had a flagship, named Ops (‘Wealth’) (CIL x 3560, 3611) which was a six (three-level, two men to an oar).We know the names of eighty-eight ships in the Misenum fleet: one six, one quinquereme, ten quadriremes, fifty-two triremes and fifteen smaller vessels (liburnae). Since the names may have been passed down from ship to ship, this may reflect the actual strength of the fleet, and accords with other evidence for its size. For the Ravenna fleet we know the names of two quinqueremes, six quadriremes, twenty-three triremes and four liburnae, which suggests that it may have been around half the size of the Misenum fleet.
Sailors served for twenty-six years (twenty-eight in the third century) and were rewarded with Roman citizenship after that time. They were also organized much like the auxilia. The sailors even call themselves ‘soldiers’ (milites) on inscriptions, and no distinction appears to have been made between rowers and marines. We find the usual immunes, as well as tesserarii, sub-optiones and optiones, signiferi and vexillarii. In addition, however, we also find specifically nautical principales, such as celeustae or pausarii who called time to the rowers, proretae (bow-officers) and gubernatores (helmsmen). Individual ships were commanded by trierarchi and squadrons were commanded by a nauarchus, the senior of whom was the nauarchus princeps. All these last three appear to have ranked as centurions, and may even refer to themselves as such on occasion, although some scholars believe that the fleet centuriones were specifically officers of marines.
All the fleets were commanded by equestrian praefecti, mostly ranking with junior procurators and just above the third grade of the militia equestris (though under Claudius and Nero many procurators were still ex-slaves of the emperor, and some of these were given fleet commands). The involvement of the Misenum and Ravenna fleets in the Civil War of ad 68–9, however, ensured that their special importance had to be acknowledged. Vespasian gave them both the honorific title praetoria, and they were subsequently entrusted to equestrian prefects who ranked only just below the prefect of the vigiles and the other great prefectures. The prefect of the Misenum fleet in ad 79 was the author Pliny the Elder, who died when he took his ships across the bay of Naples to rescue some friends from the eruption of Vesuvius in that year. The dramatic story is told in a letter (Ep. 6.16) written by his nephew, Pliny the Younger.