Jovian had surrendered Rome's much disputed claim to control over Armenia in 363, and Shapur II, being eager to make good on this new opportunity, had begun enticing Armenian lords over to his camp, eventually forcing the defection of the Arsacid Armenian king, Arshak II, whom he had quickly arrested and incarcerated.

Shapur had then sent an invasion force to seize Caucasian Iberia and a second to besiege Arshak's son, Pap, in the fortress of Artogerassa, probably in 367.

By the following spring, Pap has engineered his escape from the fortress and flight to Valens, whom he seems to have met at Marcianople, Valens’s winter quarters, while campaigning against the Goths.

A Danube flood in spring 368 prevents Valens from crossing; instead the emperor occupies his troops with the construction of fortifications.

Valens next wages war on the Thervings, now settled agriculturists in Dacia, who had aided Procopius and are threatening to invade Thrace.

The Tervingi, at this time under the leadership of Athanaric, had apparently remained peaceful since their defeat under Constantine in 332.

The Emperor, furious at their support of the late would-be usurper, crosses the Danube in May 367 and devastates the Gothic territories in modern Romania.

The Thervings flee into the Carpathian Mountains, and elude Valens' advance, forcing him to return later in the summer.

Julian had recalled Aëtius of Antioch from exile, bestowed upon him an estate in Lesbos, and retained him for a time at his court in Constantinople.

Having been consecrated as a bishop, Aëtius had used his office in the interests of Arianism by creating other bishops of that party.

At the accession of Valens in 364, Aëtius had retired to his estate at Lesbos, but soon returned to Constantinople, where he dies in 367.

Eunomius of Cyzicus, deposed from his bishopric by Constantius for his extreme Arianist views, had resided in Constantinople during the reigns of Julian and Jovian, in close intercourse with his mentor Aëtius, consolidating an heretical party and consecrating schismatical bishops.

He had then gone to live at Chalcedon, whence in 367 he is banished to Mauretania for harboring the rebel Procopius.

He is recalled, however, before he reaches his destination.

Valentinian I Strengthens the Line of Succession: The Proclamation of Gratian as Co-Emperor (367 CE)

In an effort to secure the imperial succession, Emperor Valentinian I proclaimed his eight-year-old son, Gratian, as co-emperor (Augustus) on August 24, 367 CE. This move was intended to reinforce dynastic stability, ensuring that Valentinian’s family retained control over the Western Roman Empire.

1. The Political and Military Context

• By 367 CE, Valentinian had successfully defended Gaul and Britain from barbarian incursions, but he remained concerned about the long-term stability of the empire.
• The empire was already divided into East and West, with his brother Valens ruling the Eastern Empire.
• By elevating Gratian, Valentinian established a direct hereditary succession, reducing the risk of civil war upon his death.

2. The Education of Gratian and the Role of Ausonius

• Recognizing the importance of a well-educated emperor, Valentinian entrusted Gratian’s education to Decimus Magnus Ausonius, a renowned poet, scholar, and teacher from Burdigala (modern Bordeaux).
• Ausonius was an esteemed rhetorician and grammarian, who taught in the famous schools of Bordeaux, making him one of the most respected intellectuals of his time.
• Valentinian appointed Ausonius as Praetorian Prefect, giving him significant political influence in the imperial administration.

3. Implications of Gratian’s Appointment

• Legitimacy: Proclaiming a young co-emperor signaled dynastic continuity, reinforcing the Valentinian dynasty’s claim to power.
• Stability: By securing an heir early, Valentinian hoped to prevent succession disputes and potential usurpations.
• Eastern Relations: The move likely reassured Valens, his co-emperor in the East, that the Western Empire would remain in family hands.

4. The Legacy of Gratian’s Rule

• When Valentinian died unexpectedly in 375 CE, Gratian succeeded him as Emperor of the West, ruling alongside his younger half-brother, Valentinian II.
• Gratian’s reign (367–383 CE) was marked by:
  • Religious reforms favoring Christianity over pagan traditions.
  • Continued struggles against barbarian threats, particularly the Goths and Alemanni.
  • His eventual downfall in 383 CE, when he was overthrown by the usurper Magnus Maximus.

5. Conclusion: Valentinian’s Attempt to Secure the Dynasty

By elevating Gratian as co-emperor in 367 CE, Valentinian hoped to ensure the continuity of his dynasty, but the political realities of the late Roman Empire made stability difficult to maintain. Despite Gratian’s formal succession, the Western Empire soon faced internal struggles and external threats, demonstrating the challenges of dynastic rule in the later Roman world.

Valentinian takes up residence at Augusta Trevorum, (present Trier, now in Germany) in late September 367.

The Roman garrison on Hadrian's Wall rebels in the winter of 367, and allows Picts from Caledonia to enter Britannia.

Simultaneously, Attacotti, Scotti from Hibernia, and Saxons from Germania, land in coordinated and pre-arranged waves on the island's midwestern and southeastern borders, respectively.

Franks and Saxons also land in northern Gaul.

These warbands manage to overwhelm nearly all of the loyal Roman outposts and settlements.

The entire western and northern areas of Britannia are overwhelmed, the cities sacked and the civilian Romano-British murdered, raped, or enslaved.

Nectaridus, the Count of the Saxon Shore, is killed and the dux britanniarum, Fullofaudes, is either besieged or captured, the remaining loyal army units staying garrisoned inside southeastern cities.

The areani or local agents whom the Romans pay to provide intelligence on barbarian movements seem to have betrayed their paymasters for bribes, making the attacks completely unexpected.

Deserting soldiers and escaped slaves roam the countryside and turn to robbery to support themselves.

Although the chaos is widespread and initially concerted, the aims of the rebels are simply personal enrichment and they work as small bands rather than larger armies.

Emperor Valentinian, campaigning against the Alamanni at the time, is unable to respond personally.

A series of commanders to act in his stead are chosen but swiftly recalled.

The first was Severus, the emperor's comes domesticorum, soon replaced by Jovinus, the magister equitum; rumors of disasters dog them, however, and almost fifteen months before a capable replacement is sent.

Jovinus' Victories Over the Alemanni and the Securing of Gaul (366–367 CE)

During the reign of Valentinian I (r. 364–375 CE), his general Jovinus achieved a series of significant victories over the Alemanni, securing the Rhine frontier and stabilizing Gaul for years. The third and most decisive battle took place at Durocatalaunum (modern Châlons-sur-Marne, France), where Jovinus inflicted heavy casualties on the Alemanni, ensuring a period of Roman dominance in the region.

1. The Alemanni Threat and Roman Response

• Throughout the mid-4th century, the Alemanni had been a persistent threat to Roman Gaul, frequently crossing the Rhine frontier and conducting raids deep into Roman territory.
• Valentinian I, a highly militarized emperor, sought to eliminate this threat, assigning Jovinus, one of his most capable generals, to lead Roman forces against the Germanic invaders.

2. The Three Victories of Jovinus Against the Alemanni

• First Engagement (c. 366 CE) – Jovinus defeated an invading Alemannic force, pushing them back across the Rhine.
• Second Engagement (c. 367 CE) – Another major Roman victory further weakened the Alemanni, limiting their ability to launch large-scale raids.
• Third Engagement at Durocatalaunum (Châlons-sur-Marne, 367 CE) –
  • This was the decisive battle in the campaign.
  • Jovinus inflicted devastating casualties, effectively breaking Alemannic resistance in Gaul.
  • The Alemanni were forced into a prolonged period of retreat, securing Roman dominance in northeastern Gaul.

3. The Consequences of Jovinus’ Victories

• Gaul was secured for years, ensuring relative stability in the province.
• The Rhine frontier was reinforced, preventing large-scale incursions from Germanic tribes.
• Valentinian I’s military strategy proved effective, strengthening Rome’s control over its western provinces.

4. Conclusion: A Critical Victory for Rome

Jovinus’ series of victories over the Alemanni, culminating in the Battle of Durocatalaunum (367 CE), marked a major success for Rome in its efforts to defend Gaul. His military skill and decisive leadership ensured that the region remained in Roman hands, delaying the barbarian pressures that would eventually contribute to the fall of the Western Roman Empire in the 5th century.

The inhabitants of southern Britain have abandoned their rural settlements for fortified urban centers in the wake of the successful seaborne attacks by the Picts of Scotland and the Scots of Ireland; commerce and agriculture suffer greatly.

There is little damage however, to towns or villas, though the frontier and forts behind it sustain severe damage.

A a relief force commanded by Count Theodosius in the spring of 368 arrives in Britannia from Gaul.

He brings with him four units, Batavi, Heruli, Iovii and Victores, as well as his son, the later Emperor Theodosius I and probably the later usurper Magnus Maximus.

He marches from Richborough to Londinium and begins to deal with the invaders.

An amnesty is promised to deserters which enables Theodosius to re-garrison abandoned forts.

A new dux britanniarum is appointed, Dulcitius, with Civilis granted vicarius status to head a new civilian administration.

By the end of the year, the barbarians have been driven back to their homelands; the mutineers have been executed; Hadrian's Wall has been retaken; and order returns to the province.

Baekje reaches its greatest geographic extent and political power under Geunchogo, expanding Baekje's territory to the north through war against Goguryeo, while annexing the remaining Mahan societies in the south in 369, completing Baekje's control over all of present-day Jeolla-do.

Gaya confederacy states west of the Nakdong River were also made Baekje dependencies.

During Geunchogo's reign, the territories of Baekje include most of the western Korean Peninsula (except the two Pyeongan provinces).

Baekje is invaded by Goguryeo in 369, but counterattacks in force at the battle of Chiyang.