The Roman navy does not get much attention in imperial histories. Nonetheless, Augustus was acutely aware that his fleets made his final victories in the Civil War possible. It was the fleet that had destroyed the power of Sextus Pompey—the last hope of those looking to restore the Republic—and secured Augustus’s base of power in the Western Mediterranean.1 Moreover, it was the fleet’s victory at the Battle of Actium that ended Mark Anthony’s bid for supreme power and gave Augustus control of an undivided empire. Despite historians’ lack of attention to Roman naval power, it was the glue that bound the Empire together. As long as Rome maintained its naval supremacy, it also retained the resilience to recover from any shock. This was demonstrated during the Crisis of the Third Century, where, despite some major naval reverses in the Black and Aegean Seas, the Empire’s overall naval dominance secured Rome’s hold on the great tax and resource spines of North Africa and Spain. It was only after the Vandals took control of the bulk of Rome’s western naval forces that the final demise of the Western Empire became inevitable.
Augustus always recognized the worth of a permanent naval establishment as an element of strategic power; given his military experience, how could it be otherwise? At the end of the Civil War he controlled fleets totaling approximately seven hundred ships, far more than were needed to enforce Rome’s will during a general peace. The surplus ships were laid up or burned, while Agrippa organized the remainder into two large imperial fleets (classis). Both of these praetorian fleets—the Classis Misenensis, stationed at Misenum (near Naples), and the Classis Revennas, at Ravenna—were based in Italy.2 The size of these fleets is unknown, but since three legions were built from their ranks without apparently disrupting naval activities, one can estimate that each fleet consisted of at least twenty thousand sailors plus a large force of marines, as well as a substantial support establishment ashore.3 This was probably enough to permanently man seventy-five to a hundred warships in each fleet.
For a brief time there was a third smaller fleet, made up of ships captured from Mark Anthony, stationed at Forum Julii in southeastern France, but by the time Claudius was emperor it had vanished.4 Over the decades many other fleets and bases were established around the Mediterranean. These included the great provincial fleets, such as those mentioned by Tacitus. One such fleet, the Classis Germanic, is first mentioned in 69 CE, when its prefect had to run for his life because the legions suspected him of assisting in the murder of the governor of Germania Inferior, Capito, whom they held in high regard.5 This fleet likely got its start as a temporary invasion fleet, built by Drusus to support military operations in 12 BCE. It was eventually based at Altenburg, just a couple miles south of the legionary base at Cologne.6 Although this fleet sometimes operated in the North Atlantic, it was mostly a fluvial fleet assigned to patrol the Rhine. Two other fluvial fleets—the Classis Pannonica and the Classis Moesica—patrolled the Danube. The Pannonian fleet, based in modern Zemun, patrolled the upper Danube, while the Moesia fleet, based in Noviodunum (modern Isaccea), was responsible for the lower stretches of the river. The dividing line between the two fleets was likely the gorge known as the Iron Gates, which now forms a long stretch of the Serbian-Romanian border.
The Classis Britannica, also first mentioned by Tacitus, most likely was initially formed to support Claudius’s invasion of Britain, although ever since the conquest of Gaul there had been substantial Roman naval activity in the region. This fleet was based at Boulogne, but sometime after Britain was conquered, probably in the second century, a second headquarters was built at Dover. For the first 250 years of the Empire the Classis Britannica was mainly employed in protecting trading ships between Britain and the Continent. During the Crisis of the Third Century the fleet broke free of Roman control and under its leader, Carausius—the self-styled “Emperor of the North”—began conducting independent operations.7 But by 300 CE both Britain and the fleet were once again firmly under imperial control.8
Besides the two main imperial fleets at Misenum and Ravenna, the Mediterranean was dotted with small fleets and naval installations. The largest of these fleets—the Classis Pontica, the Classis Syriaca, and the Classis Alexandria—controlled the Black Sea (Pontica), the Aegean and eastern Mediterranean Seas (Syriaca), and the southeastern Mediterranean and Red Seas (Alexandria).9 These fleets and their bases were maintained for nearly three centuries. But still other fleets were created, typically on an ad hoc basis, in support of specific campaigns and allowed to wither when the immediate need for them was gone. Because of their specific purpose—usually to support a new war—these fleets are commonly referred to in the literature as invasion fleets. Some of them were quite large; for instance, Drusus assembled over a thousand ships to support his operations in Germania.
During the Principate, the fleets’ key strategic role was to support the army’s operations, as there were no remaining threats to Roman naval superiority within the Mediterranean or along the frontiers.10 That does not mean the fleet was not kept busy. Besides supporting Augustus’s expansion of the Empire into the Red Sea and Crimea and to the line of the Danube, the navy kept the trade pathways clear of pirates. It is difficult to overstate the strategic impact of this: Roman naval power made it safe to trade throughout the Empire and beyond. Consequently, Mediterranean trade grew during the first two centuries of the Empire’s existence to levels not seen again until the nineteenth century. As mentioned earlier, it was this huge economic surge that supplied the taxable foundation for the maintenance of the Empire at the height of its power and glory.
Naval dominance also played a crucial role in the governance, management, and general security of the Empire, as messages, orders, supplies, trade goods, and even troops could be sent by sea or river to almost any point in the Empire in mere days, compared to overland travel, which could take as long as two months. Only at the remote edges of the Empire (e.g., deep in the African provinces) are travel times measured in weeks rather than days. It is worth comparing this to the mighty Persian Empire at its pre-Alexander peak. A limited number of messages could move by mounted carriers along the Royal Road from Susa, as the core of the Empire, to Sardis, near the edge of the Empire, in approximately nine days. But once they left the Royal Road, travel times increased dramatically. Moreover, everything else moving throughout the Empire had to move by foot or wagon. For an army or a baggage train to march from Susa to Sardis would take ninety days at a minimum. Without east-west rivers to rely on, lacking internal or surrounding seas, Persian rulers were continually fighting against local fragmentation. Moreover, when there was trouble on the edges of the Empire requiring a massive response from the core of power, it could take an exorbitant amount of time to respond. This is hardly surprising: it could take months for the Persian king to learn about a crisis, many more months to gather forces from across the Empire, and then additional months to march to the troublesome region. This strategic geography would continue to plague the Parthians and the Sassanids as they tried to counter Rome’s aggressive challenges.
With the Rhine and the Danube as major internal arteries, Rome found it much easier to concentrate forces at any point along the northern frontier. Moreover, secure river traffic made it relatively easy to supply the far-flung legions along the Rhine and the Danube.11 Even when Rome opted to move its armies overland, as it often did, the support of the fleet was crucial for immediate logistical support, as well as for massing food and other resources in the projected theater of operations. For the most part, the Empire had little need for a war fleet, since there were few if any naval threats on the frontiers and none within the core of the Empire. The only time there was a real need for large numbers of warships was for the invasion fleets that supported Trajan’s Dacian campaigns, as well as those needed to support periodic thrusts down the Euphrates to threaten the Parthian capital. Consequently, the core praetorian fleets at Ravenna and Misenum were allowed to deteriorate when much of their combat power was repeatedly sent to reinforce the invasion fleets.
When crisis struck, in the third century, the diminished Roman fleets were found wanting. As seemingly continuous civil wars drew the legions off the frontiers, the still relatively powerful fluvial fleets and their bases were exposed to barbarian attack. Moreover, the unending conflicts created a constant need for silver, manpower, and war materiel, leaving next to nothing to support the fleets. Overextended and overwhelmed, the Empire’s fleets were neglected—except as a source of manpower. Soon the diminished fleets were unable to accomplish their military tasks. Unable to patrol the rivers, the impotent fluvial fleets were forced to stand aside as large barbarian forces—sometimes described as “hordes”—broke through the Rhine and Danube barriers. What strength remained of the fleets was concentrated by Gordian III at Ephesus in the early 240s. From here they supported his assault on the Persians, who had overrun Mesopotamia and were driving toward the coast. Because of this concentration of vessels, the Black Sea fleet was so denuded as to be incapable of offering any serious resistance to Goth and Scythian invaders.
In the mid-250s the Goths demanded ships from the Bosporan Kingdom, a Roman client state that controlled Crimea and the eastern shore of the Black Sea. With their newly acquired fleet, the Goths attacked the Roman naval bases at Colchis and Trapezus before moving on in 257 to attack the rich cities of Bithynia; Chalcedon, Nicomedia, Nicaea, Cius, Apamea, and Prusa were all sacked. By 259 the Goths had penetrated the Aegean with five hundred ships before turning back to their homeland with a sizable quantity of plunder. The emperor, Valerian, who focused on the Sassanid threat after the fall of Dura-Europas in 256, was powerless to stop them. After a short respite, another tribe, the Heruli, joined by the Goths and others, appeared in 267–269 CE. According to Zosimus, the total barbarian force numbered over 300,000 and was carried on 6,000 vessels.12
Zosimus greatly exaggerated the size of the barbarian fleets and army, but it was surely a sizable force. What is important to note is that it once again broke into the Aegean with little trouble and sacked a number of cities, including Athens. This time Rome managed to collect enough ships from the Classis Alexandria and Classis Syriaca to defeat the barbarian fleets in a series of running battles; but it was their defeat on land at the Battle of Naissus that broke the back of the barbarian tribal confederations and allowed Rome to focus its energies on reconstituting the Empire.13
By the time of Diocletian’s accession to emperor and the return to the Empire of some measure of stability, Rome’s naval establishment was very much changed. The great imperial fleets were disbanded into numerous squadrons based in specific regions. Without the praetorian fleets at Ravenna and Misenum to give the navy a centralized headquarters, these squadrons soon lost their identity as part of the Roman navy and came under the control of the local senior military commander.14 Still, the new naval organization proved strong enough for the Empire to retain its naval dominance along the frontier as well as within its Mediterranean core for the next hundred years.
During this time there was at least one more great sea battle when, during the Civil War between Licinius and Constantine, in 323, Licinius tried to hold the Dardanelles with two hundred triremes. Constantine’s smaller force of more powerful individual ships won a decisive victory, forcing Licinius’s fleet to withdraw from action for the remainder of the conflict. There were also some great victories by the smaller fluvial fleets. In 357 the fleet on the Rhine helped Julian surround and destroy an invading force of Franks. In 386 the Romans concentrated their Danubian squadrons to crush a huge army of Goths attempting to cross on rafts.15
By the end of the century everything had taken a turn for the worse. In the north swarms of invaders came by sea to finally overrun the Saxon forts, and the remaining Roman naval squadrons were either destroyed or captured. Worse, in 406 the Rhine froze solid, immobilizing the fleet. The barbarians swarmed across the almost unguarded frontier and pressed deep into Gaul, permanently breaking the Rhine defenses. Among these tribes was a force of Vandals, who, in 409, crossed into Spain. There they acquired some ships and began raiding the North African coast and the Balearic Islands. In 429 they crossed into North Africa and began marching up the coast. After a slow, decade-long march of destruction, they arrived at Carthage. Here they faced a Roman army under Boniface, who decided that his mission in life was to make a bid for supreme power in Rome. Hence, he took his army to Italy and left Carthage—the greatest city in Africa—at the Vandals’ mercy. When Carthage fell in 429, the Vandals captured the bulk of Rome’s military fleet, much of its grain fleet, as well as a major port. Within that port was a sizable population of men who knew how to build and sail ships. Roman naval power was irrevocably broken in the west and soon replaced by the Vandals’ naval supremacy. For the first time in six centuries, there was a non-Roman fleet in the Mediterranean. It was an unmitigated strategic disaster: all the advantages that came with naval supremacy transferred from Rome to its enemies. Roman generals, preoccupied with the threat of Attila’s Huns, awoke to the danger too late.
The first part of this book centered on various themes that will help one grasp Roman strategic thinking and execution. Since 1976, when Edward Luttwak first published The Grand Strategy of the Roman Empire, there has been so much debate as to whether the Romans were even capable of thinking in strategic terms that it is vital to demonstrate they could do so early on. Had the Romans truly been incapable of comprehending their empire at the strategic level, there would have been no reason to write this book. Luckily, they clearly planned and operated at the strategic level for the entire existence of the Empire. The remaining chapters in this book are meant to clear the air as to the level of the strategic threats Rome faced and to present some details on what Rome had at its disposal to meet these challenges, including economic wherewithal, basic infrastructure, and its military forces.
Part II of this work employs a narrative history of the Empire to illuminate and explore how these themes dictated Roman policies and actions. This part of the book will take us from the start of the Empire through the height of its glory, and then delve into the Empire at its nadir and near dissolution during the Crisis of the Third Century. Part II is where we will discover how Rome adapted and executed its basic strategy over the course of three centuries. As the historical narrative progresses, I will pause at various points to discuss the underpinning strategic dynamics that are driving Rome’s story forward and to examine various strategic options that were available to emperors at crucial turning points. From time to time it will also be necessary to revisit some of our opening themes so as to account for changes in the challenges Rome confronted, as well as the power Rome had available to meet them.