After the death of Constantine ‘the Great’, in 337, the Roman Empire was divided between his three sons, each of whom held the rank of Augustus. Constantius II ruled the East; Constantine II, the eldest, ruled Britain, Spain and Gaul; Constans, the youngest, ruled Italy, the Balkans and Africa. In 340, Constantine II invaded Italy and was killed. Constans absorbed his territory.
Early in 343, for unknown reasons, Constans made a surprise visit to Britain:
… he did not sit and wait upon the beach until when the fair weather came the Ocean would calm the storm, but immediately just as things were, with the winter at its height and everything roused by the season to a peak of fury – clouds, icy chills and surf – without giving prior word to the cities there and without announcing the launch in advance, not wishing to be admired for his purpose before achieving his objective, he embarked a hundred men, so it is reported. He loosed the mooring cables and began cutting through the Ocean, and all immediately changed to calm. The Ocean flattened its wave and made itself smooth for the emperor’s passage, and that usual ebbing of the sea then confuted its law and held on to the land.
It did not happen then that while his passage to the island went so calmly, the return voyage turned out differently, but the second went better than the first in keeping with the proverb, so that there can be no dispute that this youthful undertaking was not without the blessing of God. If therefore after the island had rebelled, its inhabitants were holding an uprising, and the empire was being plundered, the news had arrived, and he had been seized with rage on hearing it and had thrown the die for the voyage, to report his act of daring would not have been to the credit of his resolve, but the crisis deriving from the rebels would have taken away the greater part of the glory. But in fact affairs in Britain were settled. He was completely free to enjoy the wonders of the Ocean from the land. There was no cause of anxiety compelling him to make the voyage greater than the harm he would have to suffer if he refused the trip. This was the situation and there was no necessity present, or rather there was only one necessity present, in his desire to set his hand to everything. He willingly gave himself over to the greatest dangers, as though going to suffer the greatest losses if he did not take the greatest risks.Libanius ‘Oration 59’ (Panegyric on Constantius and Constans) §§139–140
You [Constans] conquered your enemies; you have extended your authority, and so that greater glory might be added to your virtues, you have changed and scorned the order of the seasons, trampling underfoot the swelling, raging waves of Ocean in winter time, a deed unprecedented in the past, and not to be matched in the future. Beneath your oars trembled the waves of a sea still scarcely known to us, and the Briton trembled before the face of an emperor he did not expect.Julius Firmicus Maternus De Errore Profanarum Religionum §28.6
As we shall soon see, the historian Ammianus Marcellinus refers to Constans having visited Britain, but unfortunately his record of the circumstances is lost. His references, though, tend to suggest that Constans’ visit was concerned with the northern frontier. Perhaps, then, when Firmicus Maternus speaks of “the Briton” being fearful at Constans’ surprise arrival, he is referring to the Britons beyond Hadrian’s Wall. However, Libanius would appear to rule out a military campaign – indeed, it was evidently the intrepid emperor’s winter Channel-crossing (which in itself suggests urgency) that excited the imagination of the contemporary writers, rather than anything he achieved once he had arrived.
At some stage before 350, mentioned briefly by Ammianus, Gratian ‘the Elder’ (father of, future emperors, Valentinian and Valens) was posted to Britain:
… [Gratian] with the title of count … commanded the army in Britain …Ammianus Marcellinus Res Gestae XXX, 7
It is generally supposed that Gratian, since he had the rank of count (comes), brought units of the mobile field-army (comitatenses) from the Continent to Britain, to reinforce the resident garrison (limitanae), during some unrecorded crisis.[*] It is further often suggested that the crisis requiring Gratian’s posting to Britain was the same crisis that required Constans to make his journey to Britain, which may, or may not, be the case.
In 350 Constans was overthrown by the usurper Magnentius, who retained control of the West until 353, when he in turn was overthrown by Constantius II. Ammianus Marcellinus, within the first few extant pages of his history, writes:
… his [Constantius’] harsh cruelty, whenever the majesty of the empire was said to be insulted, and his angry passions and unfounded suspicions were increased by the bloodthirsty flattery of his courtiers, who exaggerated everything that happened and pretended to be greatly troubled by the thought of an attempt on the life of a prince on whose safety, as on a thread, they hypocritically declared that the condition of the whole world depended.…
Prominent among these was the state secretary Paulus, a native of Spain, a kind of viper, whose countenance concealed his character, but who was extremely clever in scenting out hidden means of danger for others. When he had been sent to Britain to fetch some officers who had dared to conspire with Magnentius, since they could make no resistance he autocratically exceeded his instructions and, like a flood, suddenly overwhelmed the fortunes of many, making his way amid manifold slaughter and destruction, imprisoning freeborn men and even degrading some with handcuffs; as a matter of fact, he patched together many accusations with utter disregard of the truth, and to him was due an impious crime, which fixed an eternal stain upon the time of Constantius. Martinus, who was governing those provinces on behalf of the prefects,[*] deeply deplored the woes suffered by innocent men; and after often begging that those who were free from any reproach should be spared, when he failed in his appeal he threatened to retire, in the hope that, at least through fear of this, that malevolent man-hunter might finally cease to expose to open danger men naturally given to peace. Paulus thought that this would interfere with his profession, and being a formidable artist in devising complications – for which reason he was nicknamed ‘the Chain’ – since the vicarius [i.e. Martinus] continued to defend those whom he was appointed to govern, Paulus involved even him in the common peril, threatening to bring him also in chains to the emperor’s court, along with the tribunes and many others. Thereupon Martinus, alarmed at this threat, and thinking swift death imminent, drew his sword and attacked that same Paulus. But since the weakness of his hand prevented him from dealing a fatal blow, he plunged the sword which he had already drawn into his own side. And by that most ignominious death there passed from life a most just ruler, who had dared to lighten the unhappy lot of many. After perpetrating these atrocious crimes, Paulus, stained with blood, returned to the emperor’s camp, bringing with him many men almost covered with chains and in a state of pitiful filth and wretchedness. On their arrival, the racks were made ready and the executioner prepared his hooks and other instruments of torture. Many of the prisoners were proscribed, others driven into exile; to some the sword dealt the penalty of death. For no one easily recalls the acquittal of anyone in the time of Constantius when an accusation against him had even been whispered.Ammianus Marcellinus Res Gestae XIV, 5
On 6th November 355, Constantius appointed his cousin, Julian, Caesar. Julian was despatched to Gaul:
… at a time when the barbarians had stormed many towns and were besieging others, when there was everywhere direful devastation, and when the Roman empire was tottering in evident distress.Eutropius Breviarium Ab Urbe Condita X, 14
Roman Britain, though, must have been at this time, by and large, free of predation by German pirates, since it was able to export large quantities of grain to Gaul. Just how vital these supplies were is revealed in several literary references to Julian’s campaigns against the German ‘barbarians’ – including one by Julian himself:
Then followed the second and third years of that campaign [358 and 9], and by that time all the barbarians had been driven out of Gaul, most of the towns had been recovered, and a whole fleet of many ships had arrived from Britain. I had collected a fleet of six hundred ships, four hundred of which I had had built in less than ten months, and I brought them all into the Rhine, no slight achievement, on account of the neighbouring barbarians who kept attacking me.… I marched against them, and since the gods protected me and were present to aid,[*] I received the submission of part of the Salian tribe [of Franks], and drove out the Chamavi and took many cattle and women and children. And I so terrified them all, and made them tremble at my approach that I immediately received hostages from them and secured a safe passage for my food supplies.Julian Letter to the Athenians
He [Julian] took thought for the largest island under the sun [i.e. Britain], which Ocean surrounds, and sent accountants to examine the expenditure that in theory was devoted to military operations, but in fact formed a source of income for the generals. Those guilty of this he brought to heel, and in addition he effected another far greater benefit, especially from the point of view of Gaul.
In earlier times corn was shipped from the island, first over the sea and then up the Rhine, but since the barbarians had become a force to be reckoned with, they had blocked its transport and the cargo vessels had long been hauled ashore and had rotted away. A few still plied, but since they discharged their cargo in coastal ports, it was necessary to transport the grain by waggon instead of by river, and this was a very expensive affair. Julian therefore revived the practice and considered it a serious matter should he not put the carriage of grain on its former footing. He quickly produced more ships than before and examined the ways the river might be opened up for corn.Libanius ‘Oration 18’ (Funeral Oration on Julian) §§82–83 (365)
… Julian, since the season of the year was favourable , called together his soldiers from all quarters for a campaign, and set forth; and he thought that above all things he ought betimes to attend to this, namely, before the heat of battle to enter the cities long since destroyed and abandoned, regain and fortify them, and even build granaries in place of those that had been burned, in which he could store the grain which was regularly brought over from Britain; and both things were accomplished sooner than anyone expected. For not only did the granaries quickly rise, but a sufficiency of food was stored in them; and the cities were seized, to the number of seven …Ammianus Marcellinus Res Gestae XVIII, 2
When Julian invaded enemy territory and the Chamavi begged him to spare it as though it were friendly territory, Julian agreed.… Since they were prepared to carry out all his instructions, and Julian saw that from his own point of view peace was opportune and necessary – for without the cooperation of the Chamavi it was impossible for grain from the island of Britain to be transported to the Roman garrisons – he was induced by necessity to grant them peace, demanding hostages as a surety of their good faith.Eunapius of Sardis Chronicle ‘Fragment 12’ (Müller)
… [having] restored as many captives as it was probable had been taken out of the forty cities which they had sacked, Caesar was at a loss what course to adopt, perceiving the cities to be completely ruined, and that the land had remained long without cultivation, which occasioned great scarcity of provisions among those who were delivered up by the barbarians.… Having therefore deliberated on what course to pursue he formed this plan. As the Rhine discharges itself at the extremity of Germany into the Atlantic Ocean, and the island of Britain is about nine hundred stadia [approx. 103 miles] from its mouths, he cut timber from the woods on the banks of the river, and built eight hundred vessels, larger than galleys, which he sent into Britain for a supply of corn, and brought it up the Rhine. This was so often repeated, the voyage being short, that he abundantly supplied those who were restored to their cities with sufficiency for their sustenance …Zosimus New History III, 5
The south of Roman Britain may have been, for the time being, free from barbarian raids, but in the north of the diocese it was a different story:
But in Britain in the tenth consulship of Constantius and the third of Julian [i.e. in 360] raids of the savage tribes of the Scots and the Picts, who had broken the peace that had been agreed upon, were laying waste the regions near the frontiers, so that fear seized the provincials, wearied as they were by a mass of past calamities.[*] And Julian, who was passing the winter in Paris and was distracted amid many cares, was afraid to go to the aid of those across the sea, as Constans once did (as I have told), for fear of leaving Gaul without a ruler at a time when the Alamanni were already roused to rage and war. Therefore he decided that Lupicinus, who was at that time commander-in-chief, should be sent to settle the troubles either by argument or by force; he was indeed a warlike man and skilled in military affairs, but one who raised his brows like horns and ranted in the tragic buskin (as the saying is), and about whom men were long in doubt whether he was more covetous or more cruel. Therefore, taking the light-armed auxiliaries, to wit the Heruli, the Batavians, and two companies of Moesians, in the dead of winter the leader aforesaid came to Bononia [Boulogne], and after procuring ships and embarking all his troops, he waited for a favourable breeze and then sailed to Rutupiae [Richborough], which lay opposite, and went on to Lundinium [London], intending there to form his plans according to the situation of affairs and hasten quickly to take the field.Ammianus Marcellinus Res Gestae XX, 1
Meanwhile, in Paris, in February 360, Julian was acclaimed Augustus by his troops. Julian feared Lupicinus’ opposition, and had him arrested as soon as he set foot back in Gaul. There is no record of what Lupicinus achieved in Britain, but, in a letter written in 361, Julian summarized his own achievements in Gaul:
It would take too long to enumerate everything and to write down every detail of the task that I accomplished within four years. But to sum it all up: Three times, while I was still Caesar, I crossed the Rhine; twenty thousand persons who were held as captives on the further side of the Rhine I demanded and received back; in two battles and one siege I took captive ten thousand prisoners, and those not of unserviceable age but men in the prime of life; I sent to Constantius four levies of excellent infantry, three more of infantry not so good, and two very distinguished squadrons of cavalry. I have now with the help of the gods recovered all the towns, and by that time I had already recovered almost forty.Letter to the Athenians
Julian rejected Christianity – he is commonly called Julian the Apostate – and he is the only pagan Roman emperor after the time of Constantine the Great. In 361, Julian marched east to confront Constantius, but, as luck would have it, Constantius died before the two emperors could meet in battle. It is alleged that he nominated Julian as his successor with his last words.[*] In 363, Julian mounted an ambitious campaign against the Persians. He was mortally wounded on 26th June.
Jovian – an army officer who had been hastily acclaimed emperor following Julian’s death – died after a reign of not quite eight months. Another officer, Valentinian, was selected to be Jovian’s successor. His inauguration took place on 26th February 364, at Nicaea (now İznik, Turkey). A month later, at Constantinople (Istanbul), Valentinian made his brother, Valens, co-Augustus.
At this time, as if trumpets were sounding the war-note throughout the whole Roman world, the most savage peoples roused themselves and poured across the nearest frontiers. At the same time the Alamanni were devastating Gaul and Raetia, the Sarmatae and Quadi Pannonia, while the Picts, Saxons, Scots and Attacotti were harassing the Britons with constant disasters. The Austoriani and other Moorish tribes raided Africa more fiercely than ever and predatory bands of Goths were plundering Thrace and [ ? ]. The king of the Persians was laying hands on Armenia, hastening with mighty efforts to bring that country again under his sway, under the false pretext that after the death of Jovian, with whom he had concluded a treaty of peace, nothing ought to prevent his recovery of what he claimed had formerly belonged to his forefathers.Ammianus Marcellinus Res Gestae XXVI, 4
Rule of the Empire was divided – Valens taking the East, Valentinian the West.
… [Valentinian] had no sooner begun to reign than he went to Gaul, to fortify the strongholds and cities lying near the rivers; for these were exposed to the raids of the Alamanni, who were raising their heads higher after learning of the death of the emperor Julian, who was absolutely the only one whom they feared after the death of Constans.Ammianus Marcellinus Res Gestae XXX, 7
In 367 Roman Britain faced a crisis, often called, after Ammianus’ phraseology, the Barbarian Conspiracy:
Having set out then from Ambiani [Amiens] and hastening to Treveri [Trier], Valentinian was alarmed by serious news which showed that Britain was brought into a state of extreme need by a barbarian conspiracy, that Nectaridus, count of the seacoast region, had been killed, and that the duke, Fullofaudes, had been ambushed by the enemy and taken prisoner.[*] This report aroused great horror, and the emperor sent Severus, who at that time was still count of the household troops, to set right the disasters, if chance should offer the desired opportunity. But he was recalled a little later, and Jovinus – – – having set out for the same regions, [Valentinian?] allowed them to return at quick step, intending to seek the support of a strong army; for he declared that this was demanded by the pressing necessities of the situation. Finally, because of the many alarming things which constant rumours reported about that same island, Theodosius, a man most favourably known for his services in war, was chosen to be sent there with all speed, and having enrolled legions and cohorts of courageous young men, he hastened to depart, preceded by brilliant expectations.
(See The Roman Army in Britain, Part II.) Of course, there are always dissenting voices, and Ian Hughs, in Chapter 5 of his Imperial Brothers: Valentinian, Valens and the Disaster at Adrianople (2013), argues that it is not relevant to consider the Notitia Dignitatum in this context, and, radically, suggests that: “It is more likely that Nectaridus and Fullofaudes were killed by Saxon and Frankish raiders along the coast of Gaul, rather than by enemies in Britain.” In this scenario, the expeditions of Severus and Jovinus are to the coast of Gaul – it is only Theodosius who is despatched to Britain. Incidentally, Ammianus completed his Res Gestae (c.390) during the reign of Theodosius the Great – son of the general sent to Britain by Valentinian. It is perhaps, therefore, unsurprising that Ammianus’ report on the elder Theodosius’ activities has a somewhat hagiographical flavour.
And, since in giving an account of the history of the emperor Constans I described the ebb and flow of the ocean and the situation of Britain, as well as my powers permitted, I have thought it superfluous to unfold again what has once been set forth, just as Homer’s Ulysses among the Phaeacians shrinks from repeating the details of his adventures because of the excessive difficulty of the task.
It will, however, be in place to say, that at that time the Picts, divided into two tribes, called Dicalydones and Verturiones, as well as the Attacotti, a warlike race of men, and the Scots, were ranging widely and causing great devastation; while the Gallic regions, wherever anyone could break in by land or by sea, were harassed by the Franks and their neighbours, the Saxons, with cruel robbery, fire, and the murder of all who were taken prisoners.
In order to prevent these outrages, if favourable fortune gave an opportunity, that most energetic leader hastened to the world’s end, and reached the coast of Bononia [Boulogne], which from the spacious lands opposite is separated only by a narrow space of sea wont in turn to swell with dreadful surges, and again, without any danger for sailors, to sink to the form of a level plain. From there he quietly crossed the strait and landed at Rutupiae [Richborough], a quiet haven on the opposite coast.
When the Batavi, Heruli, Jovii, and Victores, who followed him, had arrived, troops confident in their strength, he began his march and came to the old town of Lundinium, which later times called Augusta [i.e. London]. There he divided his troops into many parts and attacked the predatory bands of the enemy, which were ranging about and were laden with heavy packs; quickly routing those who were driving along prisoners and cattle, he wrested from them the booty which the wretched taxpayers had lost. And when all this had been restored to them, except for a small part which was allotted to the wearied soldiers, he entered the city, which had previously been plunged into the greatest difficulties, but had been restored more quickly than rescue could have been expected, rejoicing and as if celebrating an ovation.
While he lingered there, encouraged by the successful outcome to dare greater deeds, he carefully considered what plans would be safe; and he was in doubt about his future course, since he learned from the confessions of the captives and the reports of deserters that the widely scattered enemy, a mob of various tribes and frightfully savage, could be overcome only by secret craft and unforeseen attacks. Finally, he issued proclamations, and under promise of pardon summoned the deserters to return to service, as well as many others who were wandering about in various places on furlough. In consequence of this demand and strongly moved by his offer, most returned, and Theodosius, relieved of his anxious cares, asked that Civilis be sent to him to govern Britain as deputy-prefect [i.e. vicarius], a man of somewhat fiery temper, but steadfast in justice and uprightness, and also Dulcitius, a general distinguished for his knowledge of the art of war.Ammianus Marcellinus Res Gestae XXVII, 8
The next year:
… Theodosius, that leader of celebrated name, filled with courageous vigour sallied forth from Augusta, which was earlier called Lundinium, with a force which he had mustered with energy and skill, and rendered the greatest aid to the troubled and confused fortunes of the Britons. He secured beforehand everywhere the places suitable for ambushing the barbarians, requiring nothing of the common soldiers in which he himself did not smartly take the first tasks. In this way, while he performed the duties of an active common soldier and observed the care of a distinguished general, after having routed and put to flight tribes which an insolence fostered by impunity was inflaming with a desire to attack the Romans, he completely restored the cities and forts which had been founded to secure a long period of peace, but had suffered repeated misfortunes.
And the more to inflame thy heart with love of battle he [Honorius’ father] would recount to thee the deeds of thy grandsire, object of dread to Libya’s sun-scorched shores and Thule whither no ship can sail. He conquered the fleet Moors and the well-named Picts; his roaming sword pursued the flying Scot; his adventurous oars broke the surface of the northern seas.Panegyric on the Third Consulship of Honorius (396), lines 51–56
Hence [from Spain] came Theodosius, grandfather of Honorius, for whom, exultant after his northern victories, Africa twined fresh laurels won from the Massylae. ’Twas he who pitched his camp amid the snows of Caledonia, who never doffed his helmet for all the heat of a Libyan summer, who struck terror with the Moors, brought into subjection the coasts of Britain and with equal success laid waste the north and the south. What avail against him the eternal snows, the frozen air, the uncharted sea? The Orcades [Orkneys] ran red with Saxon slaughter; Thule was warm with the blood of Picts; ice-bound Hibernia [Ireland] wept for the heaps of slain Scots.Panegyric on the Fourth Consulship of Honorius (398), lines 24–33
But while he was thus engaged, a dread event had taken place, which would have resulted in grave danger, if it had not been crushed in the very beginning of its attempt. A certain Valentinus, born in Valeria, a part of Pannonia, a man of haughty spirit … had been exiled to Britain because of a serious crime. There, impatient of quiet like a noxious beast, he roused himself to new and destructive plans, nursing a certain grudge against Theodosius, since he perceived that he was the only one who could resist his abominable designs. However, after a good deal of looking about secretly and openly, driven by the swelling gale of his vast ambition, he began to tempt exiles and soldiers by promising for bold deeds as enticing rewards as his circumstances at the time permitted. And already the time for carrying out the plans was near at hand, when that leader, eager for deeds of daring, learning of this from a prearranged source, resolved with lofty heart to punish those who were found guilty: Valentinus indeed, along with a few of his closest associates, he had consigned to the duke Dulcitius, to be punished with death; but with the military knowledge in which he surpassed all his contemporaries, he divined future dangers, and as to the rest of the conspirators forbade the carrying on of investigations, lest by spreading fear among many the disturbances in the provinces, which had just been lulled to sleep, should be revived.
Then, after the danger had been wholly removed, since it was common knowledge that propitious fortune had failed him in none of his undertakings, he turned his attention to making many necessary improvements, restoring the cities and forts of the garrison, as we have said, and protecting the frontiers with watch-posts and defence-works. And so completely did he recover a province which had passed into the enemy’s hands and restore it to its former condition, that, in the words of his report, it had a legitimate governor; and it was henceforth called Valentia, in accordance with the emperor’s wish, who, one might almost say, celebrated an ovation in his joy on hearing the priceless news.
In the midst of such important events the areani, a class of men established in early times, about which I said something in the history of Constans, had gradually become corrupted, and consequently he removed them from their posts. For they were clearly convicted of having been led by the receipt, or the promise, of great booty at various times to betray to the barbarians what was going on among us. For it was their duty to hasten about hither and thither over long spaces, to give information to our generals of the clashes of rebellion among neighbouring peoples.
After the above-mentioned affairs and other similar ones had been so brilliantly managed, Theodosius was summoned to the court, leaving the provinces dancing for joy, after distinguishing himself by many helpful victories like Furius Camillus or Cursor Papirius. And because of his general popularity he was escorted as far as the strait, where he crossed with a light wind, and came into the emperor’s company. He was received with joy and words of praise, and succeeded to the position of Jovinus, commander of the cavalry forces, whom the emperor Valentinian considered to be lacking in energy.Ammianus Marcellinus Res Gestae XXVIII, 3
In his handbook De Re Militari (Concerning Military Matters), Vegetius gives a brief, but vivid, description of the tactics employed by the Roman navy to prevent barbarian incursions into the British provinces:
Scouting skiffs are attached to the large warships, having about twenty oarsmen on each side; these the Britons call picati. They are used on occasion to perform descents or to intercept convoys of enemy ships or by studious surveillance to detect their approach or intentions. Lest patrol vessels be betrayed by their brightness, the sails and rigging are dyed Venetian blue, which resembles the ocean waves; the wax used to pay the ships’ sides is also dyed. The sailors and marines put on Venetian blue uniforms also, so as to lie hidden with greater ease when scouting by day as by night.IV, 37
In 372, Valentinian:
… made Fraomarius king of the Bucinobantes, a tribe of the Alamanni dwelling opposite Mogontiacum [Mainz]. And soon afterwards, since a recent invasion had utterly devastated that canton, he transferred him to Britain with the rank of tribune, and gave him command of a troop of the Alamanni which at that time was distinguished for its numbers and its strength.Ammianus Marcellinus Res Gestae XXIX, 4
Valentinian died on 17th November 375, at Brigetio in Pannonia (now Komárom-Szőny in Hungary), having had an apoplectic fit during negotiations with the Quadi, against whom he had been campaigning.[*] To ensure an orderly succession, Valentinian had previously (in 367) elevated his son Gratian to the rank of Augustus. Gratian, now aged sixteen, had not accompanied his father on campaign, and was over five hundred miles away, in Trier. Valentinian’s officers, off their own bat, decided that Gratian should share his rule with his four-year-old half-brother, Valentinian. Accordingly, young Valentinian, who was living with his mother only a hundred miles away, was sent for and acclaimed Augustus (Valentinian II[*]):
And although, while this was being done, there was some thought that Gratian would take it amiss that another emperor was chosen without his permission, this fear later vanished and men lived free from care, since Gratian, besides being a kindly and righteous man, loved his kinsman with great affection and saw to his education.Ammianus Marcellinus Res Gestae XXX, 10
Soon after the death of the elder Valentinian, Theodosius (who was serving in Africa) was, for uncertain reasons, executed – Ammianus does not record the event.[*] His son, also called Theodosius and also an accomplished general, retired to the family estates in Spain.
In 378, flushed with success at having soundly defeated the Lentienses, a tribe of the Alamanni, Gratian set out to help Valens inflict a decisive defeat on the Goths. Valens, however, was envious of his young nephew’s victory over the Germans. The upshot was that he didn’t wait for Gratian’s forces to arrive and, on 9th August 378, met the Goths in battle near Adrianople, Thrace (now Edirne, European Turkey). Valens’ army was routed. Valens was killed – his body was never found. Gratian summoned Theodosius from Spain, and, on 19th January 379, at Sirmium, Pannonia (now Sremska Mitrovica, Serbia), he was appointed Augustus.
Having given him [Theodosius] the government of Thrace and the eastern provinces, Gratian himself proceeded to the west of Gaul, in order, if possible, to compose affairs in that quarter.Zosimus New History IV, 24