This situation continued until the First Punic War: the main task of the Roman fleet was patrolling along the Italian coast and rivers, protecting seaborne trade from piracy. Whenever larger tasks had to be undertaken, such as the naval blockade of a besieged city, the Romans called on the allied Greek cities of southern Italy, the socii navales, to provide ships and crews.
Despite the buildup, the Roman crews remained inferior in naval experience to the Carthaginians, and could not hope to match them in naval tactics, which required great maneuverability. They therefore employed a novel weapon which transformed sea warfare to their advantage. They equipped their ships with the corvus, possibly developed earlier by the Syracusians against the Athenians. This was a long plank with a spike for hooking onto enemy ships. Using it as a boarding bridge, marines were able to board an enemy ship, transforming sea combat into a version of land combat, where the Roman legionaries had the upper hand. However, it is believed that the corvus' weight made the ships unstable, and could capsize a ship in rough seas.
Although the first sea engagement, the Battle of the Lipari Islands in 260 BC, was a defeat for Rome, the forces involved were relatively small. Through the use of the corvus, the fledgling Roman navy under Gaius Duilius won its first major engagement later that year at the Battle of Mylae. During the course of the war, Rome continued to be victorious at sea: victories at Sulci (258 BC), Tyndaris (257 BC) were followed by the massive Battle of Cape Ecnomus, where the Roman fleet under the consuls Marcus Atilius Regulus and Lucius Manlius inflicted a severe defeat on the Carthaginians. This string of successes allowed Rome to push the war further across the sea to Africa and Carthage itself. Continued Roman success also meant that their navy gained significant experience, although it also suffered a number of catastrophic losses due to storms, while conversely, the Carthaginian navy suffered from attrition.
The Battle of Drepana in 249 BC resulted in the only major Carthaginian sea victory, forcing the Romans to equip a new fleet from private donations. In the last battle of the war, at Aegates Islands in 241 BC, the Romans under Gaius Lutatius Catulus displayed superior seamanship to the Carthaginians, notably using their rams rather than the now-abandoned corvus to achieve victory.
Due to Rome's command of the seas, Hannibal, Carthage's great general, was forced to shift the strategy, bringing the war over land to the Italian peninsula. Unlike the first war, the navy played little role on either side in this war. THe only naval encounters occurred in the first years of the war at Lilybaeum (218 BC) and the Ebro River (217 BC), both resulting Roman victories. Despite an overall numerical parity, for the remainder of the war the Carthaginians did not seriously challenge Roman supremacy. The Roman fleet was hence engaged primarily with raiding the shores of Africa and guarding Italy, a task which included the interception of Carthaginian convoys of supplies and reinforcements for Hannibal's army, as well as keeping an eye on a potential intervention by Carthage's ally, Philip V. The only major action in which the Roman fleet was involved was the siege of Syracuse in 214-212 BC with 130 ships under Marcus Claudius Marcellus. The siege is remembered for the ingenious inventions of Archimedes, such as mirrors that burned ships or the so-called "Claw of Archimedes", which kept the besieging army at bay for two years. A fleet of 160 vessels was assembled to support Scipio Africanus in Africa in 202 BC, and, should his expedition fail, evacuate his men. In the event, Scipio achieved a decisive victory at Zama, and the subsequent peace stripped Carthage of its fleet.
Following the defeat of Macedon, Rome became embroiled in a war with the Seleucid Empire. This war too was decided mainly on land, although the combined Roman-Rhodian navy also achieved victories over the Seleucids at Myonessus and Eurymedon.
These victories, which were invariably concluded with the imposition of peace treaties that prohibited the maintenance even of token naval forces, spelled the disappearance of the Hellenistic royal navies, leaving Rome and her allies unchallenged at sea. Coupled with the final destruction of Carthage, and the end of Macedon's independence, by the latter half of the 2nd century BC, Roman control over all of what was later to be dubbed mare nostrum ("our sea") had been established. Subsequently, the Roman navy was drastically reduced, depending on its Greek allies to supply ships and crews as needed.
In the absence of a strong naval presence however, piracy flourished throughout the Mediterranean, especially in Cilicia, but also in Crete and other places, further reinforced by money and warships supplied by Mithridates of Pontus, who hoped to enlist them in his wars against Rome. In the First Mithridatic War, Sulla had to requisition ships wherever he could find them to counter Mithridates' fleet. Despite the makeshift nature of the Roman fleet, however, in 86 BC Lucullus defeated the Pontic navy at Tenedos.
Immediately after the war was over, a permanent force of ca. 100 vessels was established from the contributions of Rome's allied maritime states. Although sufficient against Mihtridates, this force was totally inadequate against the pirates. Over the next decade, the pirates defeated several Roman commanders, and raided unhindered even to the shores of Italy. Their activity posed a growing threat for the Roman economy, and several prominent Romans, including two praetors with the retinue and the young Julius Caesar, were captured and held for ransom. But perhaps most importantly, the pirates disrupted the Roman lifeline: the massive shipments of grain and other produce from Africa and Egypt that were needed to sustain the city's population.
The grain shortages were a major political issue, as popular discontent threatened to become explosive. In 74 BC, with the outbreak of the Third Mithridatic War, Marcus Antonius (the father of Mark Antony) was appointed praetor with extraordinary imperium, but signally failed to defeat the pirates; rather, he was defeated off Crete in 72 BC, and died shortly after. Finally, in 67 BC the Lex Gabinia was passed in the Plebeian Council, vesting Pompey with unprecedented powers and authorizing him to move against them. In a massive and concerted campaign, Pompey cleared the seas from the pirates. Afterwards, the fleet was reduced again to policing duties against intermittent piracy.
The last major campaign of the Roman navy in the Mediterranean until the 3rd century AD would be in the civil wars that ended the Republic. Sextus Pompeius, in his conflict with Octavian, had been given command of the Italian fleet by the Senate in 43 BC, and controlled the politically crucial supply of grain from Sicily to Rome. After suffering a defeat from Sextus in 42 BC, Octavian initiated massive naval armaments, aided by his closest associate, Marcus Agrippa: ships were built at Ravenna and Ostia, the new artificial harbor of Portus Julius built at Cumae, and soldiers and rowers levied, including over 20,000 manumitted slaves. Finally, Octavian and Agrippa defeated Sextus in the Battle of Naulochus in 36 BC, putting an end to all Pompeian resistance. Octavian's power was further enhanced after his victory against the combined fleets of Mark Antony and Cleopatra, Queen of Egypt, in the Battle of Actium in 31 BC, where Antony had assembled 500 ships against Octavian's 400 ships. This last naval battle of the Roman Republic definitively established Octavian as the sole ruler over Rome and the Mediterranean world. In the aftermath of his victory, he formalized the Fleet's structure, establishing several key harbors in the Mediterranean (see below). The now fully professional navy had its main duties consist of protecting against piracy, escorting troops and patrolling the river frontiers of Europe. It remained however engaged in active warfare in the periphery of the Empire.
Under Augustus and after the conquest of Egypt there were increasing demands from the Roman economy to extend the trade lanes to India. The Arabian control of all sea routes to India was an obstacle. One of the first naval operations under princeps Augustus was therefore the preparation for a campaign on the Arabian peninsula. Aelius Gallus, the prefect of Egypt ordered the construction of 130 transports and subsequently carried 10,000 soldiers to Arabia. But the following march through the desert towards Yemen failed and the plans for control of the Arabian peninsula had to be abandoned.
At the other end of the Empire, in Germania, the navy played an important role in the supply and transport of the legions. In 15 BC an independent fleet was installed at the Lake Constance. Later, the generals Drusus and Tiberius used the Navy extensively, when they tried to extend the Roman frontier to the Elbe. In 12 BC Drusus ordered the construction of a fleet of 1,000 ships and sailed them along the Rhine into the North Sea. The Frisians and Chauci had nothing to oppose the superior numbers, tactics and technology of the Romans. When these entered the river mouths of Weser and Ems, the local tribes had to surrender.
In 5 BC the Roman knowledge concerning the North and Baltic Sea was fairly extended during a campaign by Tiberius, reaching as far as the Elbe: Plinius describes how Roman naval formations came past Heligoland and set sail to the north-eastern coast of Denmark, and Augustus himself boasts in his Res Gestae: "My fleet sailed from the mouth of the Rhine eastward as far as the lands of the Cimbri to which, up to that time, no Roman had ever penetrated either by land or by sea...". The multiple naval operations north of Germania had to be abandoned after the battle of the Teutoburg Forest in the year 9 AD.
In the years 15 and 16, Germanicus carried out several fleet operations along the rivers Rhine and Ems, without permanent results due to grim Germanic resistance and a disastrous storm. By 28, the Romans lost further control of the Rhine mouth in a succession of Frisian insurgencies. From 37 to 85, the Roman navy played an important role in the Roman conquest of Britain. Especially the classis Germanica rendered outstanding services in multitudinous landing operations. In 46 a naval expedition made a push deep into the Black Sea region and even travelled on the Tanais. By 57 an expeditionary corps reached Chersonesos (see Charax, Crimea).
It seems that under Nero the navy obtained strategically important positions for trading with India; but there was no known fleet in the Red Sea. Possibly, parts of the Alexandrian fleet were operating as escorts for the Indian trade. In the Jewish revolt, from 66 to 70, the Romans were forced to fight Jewish ships, operating from a harbour in the area of modern Tel Aviv, on Israel's Mediterranean coast. In the meantime several flotilla engagements on the Sea of Galilee took place.
In 68, as his reign became increasingly insecure, Nero raised legio I Adiutrix from sailors of the praetorian fleets. After Nero's overthrow, in 69, the "Year of the four emperors", the fleets supported Emperor Otho against the usurper Vitellius, and after his eventual victory, Vespasian formed another legion, legio II Adiutrix, from their ranks.
In the years 82 to 85, the Romans under Gnaeus Julius Agricola launched a campaign against the Caledonians in modern Scotland. In this context the Roman navy significantly escalated activities on the eastern Scottish coast. Simultaneously multiple expeditions and reconnaissance trips were launched. During these the Romans would capture the Orkney Islands (Orcades) for a short period of time and obtained information about the Shetland Islands. There is some speculation about a Roman landing in Ireland, based on Tacitus reports about Agricola contemplating the island's conquest, but no conclusive evidence to support this theory has been found.
Under the Five Good Emperors the navy operated mainly on the rivers; so it played an important role during Trajan's conquest of Dacia and temporarily an independent fleet for the Euphrates and Tigris rivers was founded. Also during the wars against the Marcomanni confederation under Marcus Aurelius several combats took place on the Danube and the Tisza.
Under the aegis of the Severan dynasty, the only known military operations of the navy were carried out under Septimius Severus, using naval assistance on his campaigns along the Euphrates and Tigris, as well as in Scotland. Thereby Roman ships reached inter alia the Persian Gulf and the top of the British Isles.
In 267-270 another, much fiercer series of attacks took place. A fleet comprised of Heruli and other tribes raided the coasts of Thrace and the Pontus. Defeated off Byzantium by general Venerianus, the barbarians fled into the Aegean, and ravaged many islands and coastal cities, including Athens and Corinth. As they retreated northwards over land, they were defeated by Emperor Gallienus at Nestos. However, this was merely the prelude to an even larger invasion that was launched in 268/269: several tribes banded together (the Historia Augusta mentions Scythians, Greuthungi, Tervingi, Gepids, Peucini, Celts and Heruli) and allegedly 2,000 ships and 325,000 men strong, raided the Thracian shore, attacked Byzantium and continued raiding the Aegean as far as Crete, while the main force approached Thessalonica. Emperor Claudius II however was able to defeat them at the Battle of Naissus, ending the Gothic threat for the time being.
Barbarian raids also increased along the Rhine frontier and in the North Sea. Eutropius mentions that during the 280s, the sea along the coasts of the provinces of Belgica and Armorica was "infested with Franks and Saxons". To counter them, Maximian appointed Carausius as commander of the British Fleet. However, Carausius rose up in late 286 and seceded from the Empire with Britannia and parts of the northern Gallic coast. With a single blow Roman control of the channel and the North Sea was lost, and emperor Maximinus was forced to create a completely new Northern Fleet, but in lack of training it was almost immediately destroyed in a storm. Only in 293, under Caesar Constantius Chlorus did Rome regain the Gallic coast. A new fleet was constructed in order to cross the Channel, and in 296, with a concentric attack on Londinium the insurgent province was retaken.
By the end of the 3rd century, the Roman navy had declined dramatically. Although Emperor Diocletian is held to have strengthened the navy, and increased its manpower from 46,000 to 64,000 men, the old standing fleets had all but vanished, and in the civil wars that ended the Tetrarchy, the opposing sides had to mobilize the resources and commandeered the ships of the Eastern Mediterranean port cities. These conflicts thus brought about a renewal of naval activity, culminating in the Battle of the Hellespont in 324 between the forces of Constantine I under Caesar Crispus and the fleet of Licinius, which was the only major naval confrontation of the 4th century.
Vegetius, writing at the end of the 4th century, testifies to the disappearance of the old praetorian fleets in Italy, but comments on the continued activity of the Danube fleet. In the 5th century, only the eastern half of the Empire could field an effective fleet, as it could draw upon the maritime resources of Greece and the Levant. Although the Notitia Dignitatum still mentions several naval units for the Western Empire, these were apparently too depleted to be able to carry out much more than patrol duties. At any rate, the rise of the naval power of the Vandal Kingdom under Geiseric in North Africa, and its raids in the Western Mediterranean, were practically uncontested. Although there is some evidence of West Roman naval activity in the first half of the 5th century, this is mostly confined to troop transports and minor landing operations. The historian Priscus and Sidonius Apollinaris affirm in their writings that by the mid-5th century, the Western Empire essentially lacked a war navy. Matters became even worse after the disastrous failure of the fleets mobilized against the Vandals in 460 and 468, under the emperors Majorian and Anthemius.
For the West, there would be no recovery, as the last Western Emperor, Romulus Augustulus, was deposed in 476. In the East however, the classical naval tradition survived, and in the 6th century, a standing navy was reformed. The East Roman (Byzantine) navy would remain a formidable force in the Mediterranean until the 11th century.
The bulk of a ship's crew was formed by the rowers the remiges (sing. remex) or eretai in Greek. Despite popular perception, the Roman fleet relied throughout its existence on rowers of free status, and galley slaves were usually not put at the oars, except in times of pressing manpower demands or extreme emergency, and even then, they were employed after they had been freed. In Imperial times, non-citizen freeborn provincials (peregrini), chiefly from nations with a maritime background such as Greeks, Phoenicians, Syrians and Egyptians formed the bulk of the fleets' crews.
During the early Principate, a ship's crew, regardless of its size, was organized as a centuria. Crewmen could sign on as marines, rowers/seamen, craftsmen and various other jobs, though all personnel serving in the imperial fleet were classed as milites ("soldiers"), regardless of their function; only when differentiation was required, the adjectives classiarius or classicus were added. Along with several other instances of prevalence of army terminology, this testifies to the lower status of the naval personnel, who were inferior to the auxiliaries and the legionaries. Emperor Claudius first gave legal privileges to the navy's crewmen, enabling them to receive Roman citizenship after their period of service. This period was initially set at a minimum of 26 years (one year more than the legions), and was later expanded to 28. Upon honorable discharge (honesta missio), the sailors received a sizable cash payment as well.
Among the crew were also a number of principales (junior officers) and immunes (specialists exempt from certain duties). Some of these positions, mostly administrative, were identical to those of the army auxiliaries, while some (mostly of Greek provenance) were peculiar to the fleet. An inscription from the island of Cos, dated to the First Mithridatic War, lists us a ship's officers, the nautae: the gubernator (kybernētēs in Greek) was the helmsman or pilot, the celeusta (keleustēs in Greek) supervised the rowers, a proreta (prōreus in Greek) was the look-out stationed at the bow, a pentacontarchos was apparently a junior officer, and an iatros (Lat. medicus), a ship's doctor.
Each ship was commanded by a trierarchus, while squadrons were put under a nauarchus, who often appears to have risen from the ranks of the trierarchi. The post of nauarchus princeps appeared later in the Imperial period, and functioned either as a commander of several squadrons or an executive officer under a civilian admiral. These were professional officers, usually peregrini who had a status equal to an auxiliary centurion (and were thus increasingly called centuriones [classiarii] after ca. AD 70). Only in the 3rd century were these officers equated to the legionary centurions in status and pay, and could henceforth be transferred to a similar position in the legions.
During the Republic, command of a fleet was given to a serving magistrate or promagistrate, usually of consular or praetorian rank. In the Punic Wars for instance, one consul would usually command the fleet, and another the army. In the subsequent wars in the Eastern Mediterranean, praetors would assume the command of the fleet. However, since these men were political appointees, the actual handling of the fleets and of separate squadrons was entrusted to their more experienced legates and subordinates. It was therefore during the Punic Wars that the separate position of praefectus classis ("fleet prefect") first appeared.
Initially subordinate to the magistrate in command, after the fleet's reorganization by Augustus, the praefectus classis became procuratorial positions in charge the permanent fleets. They were initially filled either from among the Emperor's freedmen or from the equestrian class, thus securing the Emperor's control over the fleets. From the period of the Flavian emperors, only equestrians with military experience who had gone through the militia equestri were appointed. Nevertheless, the prefects remained political appointees, and despite their military experience, usually in command of army auxiliary units, their knowledge of naval matters was minimal, forcing them to rely on their professional subordinates. The difference in importance of the fleets was also reflected by the pay of the commanders. The commanders of the two praetorian fleets were procuratores ducenarii, meaning they earned 200,000 sesterces annually, the commanders of the Classis Germanica, the Classis Britannica and later the Classis Pontica were centenarii (i.e. earning 100,000 sesterces), while the other fleet commanders were sexagenarii (i.e. they received 60,000 sesterces).
The generic Roman term for an oar-driven galley warship was "long ship" (Latin: navis longa, Greek: naus makra), as opposed to the sail-driven navis oneraria, a merchant vessel, or the minor craft (navigia minora) like the scapha.
The navy consisted of a wide variety of different classes of warships, from the heavy polyremes to the light raiding and scouting vessels. During and after the Punic Wars, the mainstay of the Roman navy was the "five" or quinquereme (Gk. pentērēs), which was copied from a captured Carthaginian model, and the "four" or quadrireme (Gk. tetrērēs). Triremes continued to serve as well as a smaller, faster vessel, especially among the allied contingents. The term "trireme" can however refer to several types of ships with three oarsmen throughout the Republican and Imperial periods, and is not necessarily indicative of one particular design. In addition, the presence of two "sixes" (hexareme, Gk. hexērēs) is recorded during the Punic Wars, which were used as flagships. The Romans do not seem to have engaged in the construction of gigantic warships like their contemporary Hellenistic navies, at least until the Civil Wars.
During the final confrontation between Octavian and Mark Antony, Octavian's fleet was composed of quinqueremes, together with some "sixes" and many triremes and liburnians, while Antony, who had the resources of Ptolemaic Egypt to draw upon, fielded a fleet also mostly composed of quinquiremes, but with a sizeable complement of heavier warships, including some "tens" (Gk. dekērēs). Later historical tradition made much of the prevalence of lighter and swifter vessels in Octavian's fleet, with Vegetius even explicitly ascribing Octavian's victory to the liburnians.
This prominence of lighter craft in the historical narrative is perhaps best explained in light of subsequent developments. After Actium, the operational landscape had changed: for the remainder of the Principate, no opponent existed to challenge Roman naval hegemony, and no massed naval confrontation was likely. The tasks at hand for the Roman navy were now the policing of the Mediterranean waterways and the border rivers, suppression of piracy, and escort duties for the grain shipments to Rome and for imperial army expeditions. Lighter ships were far better suited to these tasks, and after the reorganization of the fleet, the largest ship kept in service was a hexareme, the flagship of the Classis Misenensis. The bulk of the fleets was composed of the lighter triremes and liburnians (Latin: liburna, Greek: libyrnis), with the latter apparently providing the majority of the provincial fleets. In time, the term "liburnian" came to mean "warship" in a generic sense.
In addition, there were smaller oared vessels, such as the navis actuaria, with 30 oars (15 on each bank), a ship primarily used for transport in coastal and fluvial operations, for which its shallow draught and flat keel were ideal. In late Antiquity, it was succeeded in this role by the navis lusoria ("playful ship"), which was extensively used for patrols and raids by the legionary flotillas in the Rhine and Danube frontiers.
Roman ships were commonly named after gods (Mars, Iuppiter, Minerva, Isis), mythological heroes (Hercules), geographical maritime features such as Rhenus or Oceanus, concepts such as Harmony, Peace, Loyalty, Victory (Concordia, Pax, Fides, Victoria) or after important events (Dacicus for the Dacian Wars or Salamina for the Battle of Salamis). They were distinguished by their figurehead (insigne or parasemum), and, during the Civil Wars at least, by the paint schemes on their turrets, which varied according to each fleet.
In Classical Antiquity, a ship's main weapon was the ram (rostra, hence the name navis rostrata for a warship), which was used to sink or immobilize an enemy ship by holing its hull. Its use however required a skilled and experienced crew and a fast and agile ship like a trireme or quinquireme. In the Hellenistic period, the larger navies came instead to rely on greater vessels. This had several advantages: the heavier and sturdier construction lessened the effects of ramming, and the greater space and stability of the vessels allowed the transport not only of more marines, but also the placement of deck-mounted ballistae and catapults. Although the ram continued to be a standard feature of all warships and ramming the standard mode of attack, these developments transformed the role of a warship: from the old "manned missile", designed to sink enemy ships, they became mobile artillery platforms, which engaged in missile exchange and boarding actions. The Romans in particular, being initially inexperienced at sea combat, relied upon boarding actions through the use of the corvus. Although it brought them some decisive victories, it was discontinued because it tended to unbalance the quinqueremes in high seas; two Roman fleets are recorded to have been lost during storms in the First Punic War.
During the Civil Wars, a number of technical innovations, which are attributed to Agrippa, took place: the harpago, a catapult-fired grappling hook, which was used to clamp onto an enemy ship, reel it in and board it, in a much more efficient way than with the old corvus, and the use of collapsible fighting towers placed one apiece bow and stern, which were used to provide the boarders with supporting fire.
In addition, there is significant archaeological evidence for naval activity by certain legions, which in all likelihood operated their own squadrons: legio XXII Primigenia in the Upper Rhine and Main rivers, legio X Fretensis in the Jordan River and the Sea of Galilee, and several legionary squadrons in the Danube frontier.
It is notable that, with the exception of the praetorian fleets (whose retention in the list does not necessarily signify that they were active), the old fleets of the Principate, are missing. As far as the East is concerned, we know from other sources that the Classis Alexandrina and the Classis Seleucena continued to operate, and that in ca. 400 a Classis Carpathia was detached from the Syrian fleet and based at the Aegean island of Karpathos.