by Hughes, Ian
Gelimer’s Response
At the same time as Belisarius was making tentative moves to befriend the natives, Gelimer was moving to counter the Byzantine threat. Gelimer instantly concluded that the Byzantine army would travel along the coastal road, so passing through the valley at Ad Decimum. According to the instructions that he had already sent to his brother Ammatus, the troops in Carthage began to mobilise ready to march towards Ad Decimum from the north. Gathering a force from the area of Hermione, Gelimer marched north to rendezvous with his brother at Ad Decimum.
The Deployment of Belisarius and his march towards Carthage
Waiting for news from Syllectus, Belisarius organised the army for the march on Carthage. Three hundred bucellarii were placed under the command of John the Armenian, Belisarius’ optio (‘choice’: in charge of Belisarius’ finance), with instructions to scout the way forward and report any enemy activity. He was to remain at least twenty stades, approximately 2⅓ miles, ahead of the main force.* The 600 Huns under Sinnion and Balas were ordered to guard the left flank in a similar manner to John, also remaining at least twenty stades away from the main force.
Belisarius stationed himself in the rear, along with his bucellarii and cotmtatus, his best troops. Aware that Gelimer was last reported as being in the south of the country, this position would enable Belisarius to immediately take close control of the troops who would be under threat if Gelimer was to arrive and attack the Byzantines from the rear. Furthermore, with his mounted bucellarii in attendance, he would be able to advance instantly if there was a need to support any troops further forward who came under attack.
The rest of the army marched in the centre. The fleet was ordered to keep pace with the infantry as they moved along the coast road. No flank guard was placed upon the right flank as this was resting for the most part within sight of the sea and so was protected by the fleet.
The main army now advanced to Syllectus, where the men acted in such an excellent manner that the citizens decided to give their full support to Belisarius’ venture. Furthermore, word of the restrained behaviour of the troops now paved the way for a peaceful advance towards Carthage, with the full cooperation of the towns and cities along the route.
Marching at a rate of eighty stades (approximately 9 miles) per day, the army advanced towards Carthage, staying at the towns of Leptis and Hadrumetum along the way. Finally, they came to Grasse, 350 stades (around 40 miles) from Carthage, where the Vandal king had a palace. Although Belisarius realised that the Vandals would be close, their strength and position was as yet unknown. This was now to change. As the army prepared to settle for the night at Grasse, a detachment of the Byzantine rearguard clashed with some troops sent ahead by Gelimer. After a brief skirmish, both parties retired to their camps, but Belisarius was at last certain that at least some of the Vandals were in the vicinity and closing in behind him
Belisarius was now faced with the most dangerous part of the journey to Carthage. The road ran inland while the coast curved away to the north, forming the headland of Cape Bon. This meant that the fleet would have to sail out of sight around the Cape. Unable to keep close control of the fleet, he instructed Archelaus, the prefect, and Calonymus, the admiral, to take the fleet around the headland, but to remain at least 200 stades (c.22 miles) from Carthage. Maintaining the army’s deployment as before, he set out on the morning of the fourth day on his way towards Ad Decimum. With the absence of the fleet, he had a maximum force of around 18,000 men.
The Strategies
There is no reference to the numbers of troops available to either Gelimer or his brother Ammatus at the approaching battle. With the whole army mustering, at the most, 20,000 men, due to losses in the wars with the Moors, and with 5,000 of the best men in Sardinia under Tzazon repressing the rebellion, this leaves a maximum of 15,000 men for Gelimer. Whether he was able to muster the total force is questionable. It is more likely that he had approximately two thirds of this number available, possibly 10,000 – 12,000 men. Yet even if he could have mobilised the whole available force, his tactics are likely to have remained the same; he would never have significantly outnumbered Belisarius.
Furthermore, Gelimer would still have had a major obstacle to overcome. He would find it difficult to unite his armed forces. The Byzantines were marching towards Carthage and so forming an obstacle between the south and the north. Gelimer needed a victory at Ad Decimum in order to unite his troops.
It seems likely that the majority of the troops were led by Gelimer, since otherwise he would not have had the confidence to detach Gibamundus with 2,000 troops, as will be seen later. The number of troops available to Ammatus is also unknown, but it is possible to estimate their strength. Procopius states that they were marching in groups of no more than thirty. If we allow one group per 50 yards, this computes to around 1,000 men per mile. Allowing that Ad Decimum was 8 miles from Carthage, this gives a maximum of around 8,000 men on the road. The actual figure would be significantly lower than this: the troops had to be at Ad Decimum and deployed for battle by the early afternoon, and so would have left Carthage long before noon. Consequently, they would not occupy all of the 8 miles.
The number of troops available helps to explain Gelimer’s plan for an ambush at Ad Decimum. With only 5–6,000 men himself, and with Ammatus having only around 6–7,000, he did not have the forces to face Belisarius in a pitched battle. He did, however, have enough men to mount an ambush that could potentially destroy the Byzantine army, or at least reduce their numerical superiority and weaken their morale. Furthermore, his experience of warfare against the nomadic Moors may have predisposed him to use an ambush as a natural form of warfare.
Ad Decimum was 70 stades (around 8 miles) from Carthage. According to Procopius, the road passed through a ‘narrow passage’ (Proc, Wars, III.xvii.ll) and this is where Gelimer planned to ambush the Byzantines. The plan was simple: Ammatus was to move his troops from Carthage and block the northern exit from the valley. Once the Byzantines arrived, he was to attack the head of their column and drive it back into the valley, hopefully causing confusion and disorder, possibly even forcing Belisarius to commit his reserves. Whilst this attack was going in, Gelimer was to advance from the south and attack the Byzantines from the rear. With the extra confusion and dismay at having to fight in two directions, the Byzantines would then be annihilated and the war won.
The plan was elegant and simple, but there was one drawback: a lot would depend upon the timing of the attacks and they would not be easy to synchronize. According to Procopius, there were three roads in the vicinity heading towards Carthage, none of them visible from each other due to the hilly terrain. Coordination would be extremely difficult.
The first road was the coastal route being used by the Byzantines, which passed through Ad Decimum before heading towards Carthage. Gelimer had predicted that the Byzantines would use this road, since they needed to remain in contact with their fleet. His assumption had been proved correct when his scouts had made contact on the road the previous night. Ammatus would also use this road, but approaching from the opposite direction
The centre road was the one that came up from the south, and so was the one that Gelimer was using for his advance from Hermione. This road intersected the coastal route shortly before the pass at Ad Decimum. This piece of local knowledge had determined Gelimer in his desire to fight at Ad Decimum: the Byzantines would not know that the road from Hermione intersected the coast road here and so would be taken by surprise at his unexpected appearance at the junction.
It was the third road that was to cause Gelimer anxiety. This was further inland and bypassed the valley at Ad Decimum, following a separate route towards Carthage. If Ammatus was to follow Gelimer’s instructions, Carthage would be left defenceless. With Sardinia and Tripolitania in open rebellion, Gelimer would have distrusted the natives. Even a weak Byzantine force advancing down this road would be unopposed and the Carthaginians were likely to open the gates to them. Winning
a battle at Ad Decimum would be negated if Carthage itself was in enemy hands, since this could easily provoke more areas to rebel. Accordingly, Gelimer changed his plans and sent his nephew Gibamundus on to the road to ensure that Carthage remained secure. The diversion of 2,000 men away from the battle was a small price to pay to ensure that the city remained in Vandal hands. The move would also allow Gelimer to change his plans if it revealed that either the main body or at least a large detachment of Byzantine troops had already reached this road and were advancing upon Carthage, having bypassed his intended ambush at Ad Decimum.
Procopius gives a different reason for the detachment of Gibamundus. He claims that Gibamundus was to make a wide swing to the left before moving back in and attacking the Byzantines from their flank (Procopius, III.xviii.1). On close inspection this scenario would appear unlikely, since the eastern road was too far from Ad Decimum – according to Procopius, Gibamundus was travelling northwards forty stades (approximately 4½ miles) away from the battlefield. Any troops sent on this route would have little chance of taking part in the battle, since the intervening terrain was hilly and would slow down their movement accordingly. If the troops under Gibamundus were to attack the Byzantines in the manner described by Procopius, they would have stayed with the main force until nearer to Ad Decimum before moving a short way into the hills. With only a short distance to travel, they would then have been in an ideal position to fall upon the undefended Byzantine flank.
Gelimer’s plan was relatively simple and only depended upon timing. In contrast, at no point did Belisarius want to fight a battle on that day. He still had no clear idea concerning the Vandal’s strength or army composition. What he wanted was information which he could use in order to plan a battle for the following day at the earliest.
The Battle of Ad Decimum
Although usually described as a single battle, the action was actually fought in four distinct and separate phases, all either out of line of sight of each other or at different times.
Opening Moves
Following Gelimer’s instructions, on the early morning of the fourth day after the invasion Ammatus (Gelimer’s brother) ordered his men to follow him to the pass whilst he himself went ahead to scout the area and decide upon deployment.
As the Vandals marshalled their forces and marched towards Ad Decimum, Belisarius was nearing the valley. Around four miles from Ad Decimum, the Byzantines came upon a natural position which was an ideal place to act as a camp. Setting the infantry to fortify the place, and leaving the baggage and Antonina in relative safety, Belisarius led the remainder of his cavalry out to meet the Vandals. With John and his 300 men still scouting ahead and with the Huns still guarding his left flank, Belisarius set forth on the afternoon of the fourth day since their arrival in Africa. His plan was to locate the enemy and assess the strength and the composition of their army, before retiring to the safety of the newly-built camp and deciding upon a strategy for the ensuing battle. Accordingly, he sent the foederati under Solomon (Dorotheus having died in Sicily) ahead to contact John and try to locate the Vandal forces. He was unaware that John had already made contact and that the Battle of Ad Decimum had begun.
Phase I: The Defeat of Gibamundus
According to Procopius, two engagements occurred at approximately the same time. At around noon, Gelimer’s nephew Gibamundus and his 2,000 men encountered the Huns as they travelled along the third road, close to Pedion Halon, forty stades (around 4½ miles) from Ad Decimum. Although outnumbering the Huns by odds of over three to one, the Vandals stopped when faced by a single Hun who rode ahead of his own forces and faced them alone. It is unknown why they stopped: possibly due to fear of a trap, possibly in amazement at the courage of the lone Hun, or possibly due to their surprise at finding enemy troops so far from Ad Decimum. Procopius chooses to claim that they were afraid due to the Huns’ reputation as fierce warriors. Whatever the actual reason, their failure to act put heart into the Huns and they attacked the Vandals at full speed. Without attempting to resist, Gibamundus was killed and his men routed and completely destroyed (Procopius, Wars, III.xviii. 18–20).
Phase II: The Defeat of Ammatus
Meanwhile, Ammatus had made a mistake that would prove extremely costly. Instead of gathering a large force and advancing towards Ad Decimum en masse, he had gone ahead with only a few troops to assess the proposed battlefield. The rest of his forces followed in small groups of no more than thirty men, stretching back in a long line towards Carthage.
Ammatus reached Ad Decimum around noon, at roughly the same time as Gibamundus was being defeated and killed. Unfortunately for him, he encountered John and his 300 bucellarii. Despite killing twelve of the bucellarii, Ammatus was himself killed and the remnants of his small force fled back down the road towards Carthage, with John and the bucellarii in hot pursuit.
Unable to concentrate their forces and mount a viable defence, the small groups of Vandals that the pursuing Byzantines encountered marching towards Ad Decimum abruptly turned and fled. The whole action quickly assumed a sort of domino effect. The trickle became a flood, with all of Ammatus’ forces retreating towards Carthage. John advanced as far as the gates of the city before his men halted their pursuit. The road back to Ad Decimum was now littered with the bodies of dead and dying Vandals; Procopius stated that the carnage resembled a battle fought by 20,000 assailants rather than 300 (Proc, Wars, xviii, 11). The victors slowly began to drift back along the road, looting the bodies of the Vandal dead as they went.
Phase III: The Arrival of Gelimer
Meanwhile, the Byzantine foederati under Solomon – moving in advance of Belisarius – had reached the site of the initial fighting between John and Ammatus and had found the bodies of the troops who had died, including that of Ammatus himself. After questioning local inhabitants – presumably friendly thanks to the troops’ excellent behaviour – they were at a loss as to what course to take, so climbed the nearby hills to gain a vantage point over the country thereabouts. Once on higher ground, they noticed a cloud of dust approaching from the south, following the line of the second road; it was Gelimer and the main Vandal force. The leaders of the foederati immediately sent messengers to Belisarius, urging him to march as quickly as possible to their assistance. They now argued over whether to retire or to attack the Vandals. However the decision was to be academic. In between the armies was a large hill, the highest in the area. Ideal as a place to establish a camp, with views over all of the surrounding area, individuals in both armies recognised its importance and began to fight to gain possession of the hill.
The Vandals reached the summit first and then, due to the advantage of being uphill as well as having superior numbers, their attack routed the foederati. Fleeing in panic, the foederati attempted to reach Belisarius and his reinforcements. They retreated until they reached a position held by Uliaris, the commander of Belisarius’ personal guard, along with 800 of his men. The foederati expected the guardsmen to join with them and face any further attacks, but they now received a shock: upon hearing the news of the defeat, the Guard broke and fled down the road towards Belisarius and safety.
When the fleeing troops reached Belisarius, they halted. He ordered them to reform their ranks ready for battle and then reprimanded them for their flight. Afterwards, he listened to their reports. Realising that Gelimer had halted and that a large number of Vandals had already been defeated, he believed that he outnumbered the remaining Vandal forces at Ad Decimum. With the knowledge that he had an opportunity to strike a heavy blow at the Vandals; he ordered the troops to march at full speed towards Ad Decimum.
In the meantime, Gelimer himself had a choice to make. According to Procopius, he could have either immediately pursued the foederati or moved on to Carthage. Either choice would have been a disaster for the Byzantines. Pursuit would have caught Belisarius unawares and Procopius believes that the Byzantines would have been overrun and completely defeated (Proc, Wars, III.xix.25–27). A move towards Cart
hage would have encountered John and his 300 men, now busily engaged in looting the bodies of dead Vandals. The Vandals would easily have been able to kill them all. In addition, Gelimer would have been able to capture or defeat the Byzantine fleet, which had ignored its orders and advanced to within reach of the Vandal fleet in Carthage (Proc, Wars, III.xix.27–28). Instead, Gelimer descended from the hills at walking pace and so came upon the body of his brother Ammatus. Procopius asserts that Gelimer now began mourning for his brother and arranging for his burial, while his troops aimlessly milled around in the confined space.
The assessment is at fault. Obviously, Gelimer would want to take care of his brother’s body. Yet, unlike Belisarius and Procopius, Gelimer was ignorant of the course of events. The nearby inhabitants had chosen their sides and so did not inform Gelimer of the nature of his brother’s death. Expecting to meet his brother, instead he had found the body of Ammatus alongside those of only a few Vandals and a handful of Byzantines. He would have been at a loss to understand what had happened. Gelimer could not have foreseen that the armed forces from Carthage would be defeated by only 300 men. It would be natural to assume that the Byzantines had advanced faster than expected and either the Vandal forces had immediately fled when confronted with superior numbers, or Ammatus had ordered a retreat, himself dying as part of the rearguard. Gelimer therefore believed that the main body of the Byzantines had already passed and the troops that he had defeated had been the Byzantine rearguard. The main Byzantine force would by now be approaching Carthage.