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  As night fell the Parthians broke off their attack. The dispirited Roman infantry were left to their own devices as the officers conferred. The Roman officers did not issue any orders for security, preparations to move, or even to care for the dead and wounded. Crassius himself went to sleep while his commanders discussed breaking contact and retreating to the fortified garrison at Carrhae. But they faced a dilemma: if they abandoned the injured soldiers, the complaints of the wounded might alert the Parthians. If they tried to transport the wounded, the army might not reach the city walls before daylight. They decided to leave the injured soldiers behind.

  Although a horse’s night vision is superior to that of a human, limited visibility conditions increase the horse’s propensity to be startled or spooked. This is particularly true in large groups of horses. This, combined with the human commander’s increased difficulty commanding and controlling the formation in darkness, created significant tactical challenges for mounted cavalry operations at night. Thus, for most of the history of the military horse, mounted units have limited operations at night to traveling where contact with the enemy is unlikely. Because of this the Parthian cavalry could not follow the Romans closely at night. The retreat to Carrhae was successful, although at daylight the Parthians destroyed several cohorts that got lost. The Parthians also killed the wounded left in the Roman camp. The next day the Parthian commander sent messengers to the city walls to invite Crassius to parlay. When Crassius declined, Surena knew the Roman army was inside the city, and he surrounded the town. That night, native guides betrayed the continued retreat of the Romans. Instead of guiding the legions to safety, the guides led the army into marshes where the Parthians caught up with them the next morning. Several Roman detachments, including the remaining cavalry under Cassius, broke away from the main body and made their way to the safety of more mountainous terrain.

  Crassius found himself in an exposed position with about 9,000 infantry. Surena again offered to parley with Crassius for the safe retreat of his army. As Crassius and a party of officers met with Surena a fight broke out, probably because the Parthians had planned to make Crassius a prisoner. Crassius died in the skirmish, and those of his party who survived retreated to join the remnants of the army. Surena demanded their surrender. While some capitulated, the rest fought a futile battle against the Parthian cavalry. The survivors attempted to escape during the night. Only a few were successful. The Romans lost 20,000 men; another 10,000 became prisoner over the course of the three-day battle.

  Carrhae was the first large-scale encounter between the Parthians and the Romans. Two factors account for the Roman defeat. First was the incompetent leadership of Crassius. He made poor tactical decisions, demonstrating a total lack of understanding of combined arms battle and a particular lack of appreciation for cavalry. Second, the Roman army was extremely unbalanced in terms of arms. The army did not have enough cavalry nor enough missile weapons (dismounted archers and slingers) to keep the Parthian archers at a distance. Dismounted archers, in particular, could outrange the smaller bows of mounted archers and were effective at keeping them at a distance where their arrows were useless against shields and armor. In future years, Roman encounters with the Parthians would not be so one-sided, and overconfident Parthian cataphracts were defeated by Roman infantry several times.49 As the imperial army developed alae cavalry who were disciplined and well equipped, they were able to chase off horse archers and were armored enough to break up a cataphract charge.50 The key to dealing with the Parthians, and later the Sassanians, was discipline and careful control of the army. Light infantry, archers, and cavalry had to be used to negate the effects of horse archers while not becoming exposed to a cataphract charge. The Roman heavy infantry learned to form a defensive shield against the charge of the cataphracts. But mastering the necessary complex employment of forces was not always within the capabilities of all Roman generals. Even when they achieved tactical success, Roman armies had great difficulty fixing cavalry forces and decisively defeating the Parthian armies. The Sassanians, who followed Parthia, proved even more challenging.

  In the second century AD, the Sassanians replaced the Parthians as the major power in the Middle East. The Sassanians were a much more politically cohesive power and, therefore, much more dangerous to Rome. They were able to field large, though inferior, infantry forces, as well as horse archers and cataphracts. In 241 AD, Shapur I became king of the Sassanians. Almost immediately following his ascent to the throne, a Roman army, under Emperor Gordian III, attacked. The Romans invaded the Sassanian western lands (modern-day Iraq) with the objective of capturing the capital, Ctesiphon, on the Tigris River. In 244, Shapur defeated Gordian’s army at Misiche and the Romans retreated. In 253, Sharpur went on the offensive and defeated a large Roman army of 60,000 to 70,000 troops at Barbalissos, in Mesopotamia. Shapur continued the offensive deep into Roman Syria and captured Antioch and Dura Europos in 256. A new Roman emperor, Valerian, counterattacked and pushed Shapur out of Syria. But in a second battle at Carrhae in 260 AD, Valerian and a Roman army of 70,000 were decisively defeated. The Sassanians captured Valerian alive—the only emperor ever taken prisoner—along with tens of thousands of his men.51 The Roman defeats at the hands of the Sassanian cavalry armies between 244 and 260 AD probably cost the empire more than 150,000 soldiers. By some accounts, this represented one-third of the total military strength of the empire. Historians know little about the tactical details of these Roman defeats; however, based on what is known of Roman and Sassanian fighting techniques and equipment, it is likely that the Roman cavalry simply were not equal to the Sassanians, and once the Roman cavalry were defeated, the Sassanians would have been able to wear down the Roman infantry in the great open spaces of the eastern frontier.

  The most successful Roman emperor against the Sassanians was Julian the Apostate who invaded the Sassanian Empire in 363 AD. He successfully defeated the Sassanian army several times. His legions resisted Sassanian cavalry attacks and drove their cavalry from the field. However, Julian could not achieve a decisive victory against the Sassanians, and after each defeat the Sassanian army was able to withdraw intact.52 Julian’s operations highlight the inability of the Roman cavalry to press home a pursuit. Julian’s cavalry were likely unable to match the Sassanian cavalry tactically, though Julian was able to compensate with his other arms in battle. In this regard he was far superior to his predecessors, Gordian III and Valerian, who were not as tactically skillful. In the end, however, the inability of Roman cavalry alae to match Sassanian cavalry prevented Julian from turning tactical victory into operational and strategic success. Ultimately, Julian’s army had to retreat from Persia harassed by the Sassanian cavalry and strategically defeated. The fact that the Romans did not lose a single battle was irrelevant.

  Adrianople, 378 AD

  Throughout the first and second centuries AD, the Roman imperial armies were effective at protecting the frontiers of the empire. One reason for their effectiveness was the relatively competent, though not numerous, alae. Another was the overall efficiency of the Roman military system, which recruited and equipped competent military formations—in particular exceptionally disciplined heavy infantry legions. However, beginning in the middle of the third century, the quality of Rome’s army relative to its enemies began to erode. The defeat of some of the best troops in the battles against the Sassanian Empire contributed to this decline. Various emperors attempted to reverse this trend with varying degrees of success. The military problems were symptomatic of the internal political instability of the empire. Emperor Julian’s failed invasion of Persia established Rome’s inability to intimidate the empire’s enemies and the decisive defeat of Emperor Valens by the Goths at Adrianople in 378 AD cemented the impression. The battle of Adrianople was part of the Roman effort to control the Gothic tribes crossing the Danube into the empire, and illustrates the changed nature of war and the continued inability of the Roman army’s mounted forces to provide the type of cavalry
support necessary for victory.53

  In 376 AD, the Huns were pushing the Goths south and west, and some Goth tribal leaders requested permission of the emperor to enter the empire. This was granted, but by 377 additional unauthorized crossings had occurred, and the tribes—both the legal and illegal—were starving. The Romans failed to provide farming land as promised in agreements. The tribal leaders, led by Fritigern, broke out of reservation areas south of the Danube and streamed south into Thrace in search of food and land. They hoped, at a minimum, to force the emperor to grant them their promised land.

  In 376 and 377 the Goths, though not formally organized except as tribal warrior bands, defeated Roman frontier forces and the Roman army of Thrace. Roman control was lost except in the fortified cities where Roman garrisons and citizens were secure because the Goths lacked siege skills. In 378 Emperor Flavius Iulius Valens assembled the imperial army of the eastern empire to restore Roman authority. Because the Romans judged that a single army was insufficient to subdue the Goths, the western imperial army, under Emperor Gratian, marched east to support Valens’ troops. The Roman plan was simple: join the two imperial armies, locate the major Goth force under Fritigern, destroy it in battle, and restore Roman control over Thrace.

  Valens’s scouts located the Goths’ main force and reported 10,000 Goths moving south to the rear of Valens’s army, which was moving northwest to link up with Gratian’s forces. Valens turned his army around to meet the Goths. The two armies met about eight miles southeast of Adrianople in rough, hilly terrain. Valens’s army probably numbered about 15,000 to Fritigern’s 10,000, but unknown to the Romans, Fritigern summoned several other Goth tribal bands to join him. Fritigern opened negotiations with the Romans to gain time for his reinforcements to arrive.

  As the two leaders negotiated, the armies deployed. The Romans moved from their march order into their battle line with the leading cavalry moving forward to provide security. The lead cavalry covered the infantry deploying to form the Roman center while the trail cavalry force moved forward into the left wing position. Standard procedure then called for the cavalry screen to withdraw and occupy its place as the right wing of the battle line. The Goths, typically much less structured than the Romans, massed their forces on high ground, forward of their fortified laager of baggage wagons. Within the laager were the women and children of the tribe. The majority of the Goth soldiers were on foot, but wealthier warriors were mounted.

  The leaders had completed initial negotiations, where they agreed to talk further, when the battle started. Despite the fact that the whole of the Roman army was not yet deployed, the impetuous charge of the lead Roman cavalry against the Goths’ left flank began the battle. This charge drew all the Roman right wing cavalry into the attack. The Romans successfully penetrated almost to the Goth baggage train before the Goth infantry rallied. At that point, mounted Goth reinforcements arrived on the Roman’s left flank and countercharged the tired Roman cavalry. Under this assault the Roman right wing cavalry was disordered and routed to the rear. As the right wing cavalry ran to the rear, they collided with their own left wing still moving forward into position. The left wing cavalry was disrupted, so that when the Goth mounted forces hit them they were unable to withstand the charge. As a result, they too disintegrated and fled the battlefield. As the Goth cavalry drove off the Roman cavalry, the Goth infantry, inspired by the Goth cavalry success, charged down from their elevated position into the partially formed Roman infantry ranks. The infantry battle became a push of shields and spears; neither side could gain the advantage. Roman infantry had better weapons, armor, and training while the Goths had the benefit of individual warrior skills—and the knowledge that they were fighting for their families nearby. The battle turned when the victorious Goth cavalry attacked the Roman infantry in the flank and rear. The battle took on the classic form of other decisive victories in the ancient world: the Goths gradually and systematically pressed the Roman infantry from all directions and they either died in their formations or were killed as they attempted to flee. The Roman officer and historian Ammianus described the confusion of the last minutes of the Roman eastern army:

  Dust rose in such clouds as to hide the sky, which rang with fearful shouts. In consequence it was impossible to see the enemy’s missiles in flight and dodge them; all found their mark and dealt death on every side. The barbarians poured on in huge columns, trampling down horse and man and crushing our ranks so as to make orderly retreat impossible. . . . In this scene of total confusion the infantry, worn out by toil and danger, had no strength left to form a plan. Most had their spears shattered in the constant collisions. . . . The ground was so drenched with blood that they slipped and fell . . . some perished at the hands of their own comrades. . . . The sun, which was high in the sky scorched the Romans, who were weak from hunger, parched with thirst, and weighed down by the burden of their armour. Finally our line gave way under the overpowering pressure of the barbarians, and as a last resort our men took to their heels in a general rout.54

  Emperor Valens died during this battle. According to one report the emperor died from an arrow wound while on the battlefield among the lines of the legions that did not flee. The Romans lost at least two-thirds of their force—about 10,000 men. The loss of the imperial field army left all of Roman Thrace at the mercy of the Goths. The Goths, however, were able to accomplish little except to plunder the countryside as Roman garrisons and cities were impregnable to their assaults. Eventually a new eastern emperor, Theodosius, reformed the army. The war continued for four years with neither side gaining a decisive advantage. In AD 382 a negotiated peace gave the Goths the rights to land within Thrace originally agreed upon in AD 376.

  In the battle at Adrianople Roman cavalry, for once, were not outnumbered. The Roman cavalry is likely to have been between 3,000 and 4,000 men. The Goths, because of the near-starvation conditions under which the tribes existed, did not have an abundance of horses. It is doubtful that they outnumbered the Romans, and it is likely that they had fewer cavalry than the Roman army. However, numbers did not decide the battle; the quality of command, timing, and the psychology of battle were the determining issues. The mistake that cost the lives of the entire army was the Roman cavalry commander’s inability to control his forces in the forward screen of the army’s deployment. This lack of command and control exposed the Romans to the Goth cavalry charge which established psychological dominance over the Romans, even though the Goths were not as well mounted, armed, or armored—and probably were outnumbered as well.

  In cavalry actions, the analysis of battle must take into account both the psychology of the rider and the horse. The two are closely linked. Horses sense and react to the emotional state of the rider. Confident riders can embolden their mounts. Likewise, riders who are surprised or fearful communicate this. Horses also sense the state of mind of the other horses in the herd. This is a natural protective mechanism of herd animals, and combined with the horse’s natural instinct to take flight from danger, can have important consequences in the midst of a cavalry battle.

  When the Goth cavalry charged they surprised the tired riders and mounts of the Roman cavalry. The Roman cavalrymen instantly transmitted their instinct to flee to their horses and reinforced the horses’ own instinct. Humans can recognize and control their instinctual reaction to events, but horses are much less likely to. No amount of riding skill or command orders could stop the flight impulse of the Roman horses. The Roman cavalry mounts galloping to the rear transmitted their fear to the horses of the Roman left wing cavalry moving forward, and most of that cavalry lost control of its horses and joined the herd stampeding to the rear. Controlling a cavalry force once horses sense panic is a severe test of a cavalry unit’s horsemanship and leadership. At Adrianople most of the Roman cavalry failed this test, with disastrous consequences.

  During the centuries of warfare dominated by the armies of Rome, the employment of cavalry at both the tactical and operational levels o
f war did not change significantly from that of the campaigns of Alexander. Cavalry was the most economical and decisive means of attacking infantry, as well as the most effective means of protecting it. In an infantry versus infantry battle, both sides invariably suffered significant casualties. Combining cavalry with infantry achieved victory at much less cost. At the operational level of war—that which connects battles to strategic objectives—cavalry were absolutely essential to pursue and destroy a fleeing enemy. An army that could not be completely destroyed on the battlefield had to be fought again. Cavalry were also essential to prevent surprise, to protect logistics lines and bases, and to locate the enemy. Failure of cavalry forces to accomplish any one of these tasks could result in tactical defeat in battle as well as the failure of a campaign—even if an army won all its battles.

  The Romans had an important influence on tactical cavalry combat, primarily through disseminating information about the framed saddle. This piece of equipment permitted the cavalryman to become a more reliable and effective close-combat weapon. This invention, combined with increased armor technology, resulted in the appearance of the cataphract heavy cavalry, who although they did not dominate the Roman battlefield set the stage for the increased influence of the heavily armored mounted warrior that occurred later in the Medieval period. The other important specialized cavalry whose importance would last beyond the Roman period was the mounted archer. Rome suffered in battle with cavalry armies and with mounted archers precisely because it could not match, and often could not withstand, the threat of horseman armed with bows. But the Romans demonstrated that it was also important for the bulk of the cavalry to be a multipurpose force. The cavalry of the Roman alae perfectly met this ideal. They had enough armor to participate in the main battle but were mobile enough to operate in the reconnaissance, security, or pursuit roles. When used well by Roman generals, they were an important part of the solution to mounted archers and cataphracts.