Adrianople

 (Coin of the Emperor Valens from here)

It was blazing hot on the afternoon of August 9, 378 as the army of the Eastern Roman Empire, led by the Emperor Valens, marched north from the city of Adrianople.  The city, founded or more accurately refounded, by the Emperor Hadrian (117-38) and named, not coincidentally Hadrianopolis (though its English name is Adrianople perhaps bestowed by Cockney tourists) in the Diocese of Thrace is today known as Edirne and located in European Turkey near the junction of its borders with Greece and Bulgaria.  The stunning and complete defeat of that army and the death of the Emperor later that day would set in motion the events that would lead to the end of the Western Roman Empire in the 5th century.

The Roman Empire had recovered from the turmoil and crisis of the 3rd century (see Diocletian Has A Very Good Day) but the cost of the recovery had been great.  The army was much larger, taxation greater and an administrative bureaucracy had grown based upon the idea of keeping every Roman in the same station to which they were born.  For most of the period since the late 3rd century, the Empire had been split with an Emperor ruling in the East from cities such as Sirmium, Thessalonica and Nicomedia until the capital was permanently situated in the new city of Constantinople in 330, with the Western Empire ruling from a rotating series of locations including Trier and Milan.  Even with this arrangement civil war was a constant threat and a common reality.

(from usu edu)

Valens was a product of the most recent paroxysm of internal strife.  His older brother Valentinian came to the throne in 364 upon the death of the Emperor Jovian who ruled for less than nine months after the suspicious death of the Emperor Julian (the last pagan ruler) while on campaign in Mesopotamia the prior year.  Valentinian named his younger brother as co-ruler and gave him the East while he proceeded westwards to protect the more endangered borders along the Rhine and Danube.  In 375 Valentinian died of a stroke and his 16-year old son, Gratian, became ruler in the West.

We still have one roughly contemporaneous account of these times from the historian (and ex-soldier) Ammianus Marcellinus who wrote a history of the years 96 to 378 of which the portion covering 354 to 378 survives (it is thought to have been published in the late 380s or early 390s).  It needs to be treated cautiously when evaluating its historical accuracy but it's useful to quote the author's assessment of Valens whom he describes as of dark complexion "and the sight of one eye was impaired, though this was not apparent at a distance.  He was well made, neither tall nor short, bow-legged, and with a somewhat protruding stomach" (he was about 50 at the time of his death).

On the positive side, Ammianus describes Valens as "a faithful and reliable friend" who "repressed ambitious intrigues with severity":

He maintained strict discipline in the army and the civil service, and took particular care that no one should gain preferment on the score of kinship with himself . . .  In his dealing with the provinces he showed great fairness . . . He was especially concerned to lighten the burden of tribute, and allowed no increases in taxation . . . and a harsh and bitter enemy of embezzlers and of officials detected in corrupt practices . . .  men of restless greed behaved with more restraint.

Regarding his defects Ammianus writes:

He was insatiable in the pursuit of wealth and unwilling to endure fatigue, though he affected enormous toughness.  He had a cruel streak, and was something of a boor, with little skill in the arts of either war or peace . . . he was unjust and passionate, always ready to lend an ear to the charges of informers without sifting truth from falsehood.  This is a shameful fault, and greatly to be dreaded even in private and everyday matters . . .  He was dilatory and sluggish.

In 376, ambassadors from the Gothic tribes crossed the Danube seeking asylum within the Empire.  Their request was apparently prompted by the first raids from the Huns who were moving westwards from the area of the Volga River and who would trigger further chaos and destruction over the next 75 years.  The Goths had migrated from Scandanavia and/or the southern shores of the Baltic to what is now the Ukraine during the third century and since then had moved west and south where they came into contact, often violent, with the Romans. Valens was well acquainted with the Goths having successfully campaigned against them on the northern side of the Danube in 367 and 369.
(from thenagain)

Valens accepted the offer, believing that the resettlement of the Goths in the area south of the Danube would provide a bulwark against further invasions from across the river as well as a source of manpower for his planned war against the Sassanids of Persia.  The numbers of Goths who came across the river is unknowable with estimates of up to 200,000 but it was a tribe on the move including women and children.  Troubles began almost immediately with the Roman administrators of the province providing meager rations to the Goths and actually enslaving some.  The result was that they Goths began to resort to plundering and looting their new civilian neighbors.  Repeated attempts to restore order failed and eventually Valens assembled an army of about 30-40,000 legionnaires and set out from Constantinople to confront the barbarians.

To assist his uncle, Gratian agreed to send forces from the Western Empire. By early August, Valens was at Adrianople.  Word reached him that Gratian had been delayed in moving east but would arrive within a short time and requested that his uncle wait to advance until then.  According to Ammianus, Valens called a council of war at which "the flattery of some of his courtiers prevailed.  They urged immediate action to prevent Gratian sharing in a victory which in their opinion was already as good as won".

On the morning of August 9, the Roman army advanced from Adrianople and encountered the Goths less than ten miles from the city.  The Gothic chieftain Fritigern attempted to negotiate but Roman commanders, possibly on their own initiative without orders from Valens, launched an attack.  Accounts of the battle differ on details but the end result is in no doubt.  Somewhere between two thirds and three quarters of the Roman army died as did the Emperor, whose body was never found.  It was not just the number of soldiers that died that was of import, it was that they were the pick troops of the Eastern Empire.  Ammianus wrote of the battle:

No battle in our history except Cannae [Hannibal's defeat of the Romans nearly 600 years earlier] was such a massacre, though more than once the Romans have been the playthings of fortune and suffered temporary reverses . . .

The significance of the battle is that with the loss of so many troops the Romans were never to get the Goths under complete control again and they became a constant disruptive force within the Empire for the next forty years.  For the rest of the 4th century they occupied and raided much of what is now Macedonia, Albania and northern Greece while alternating between being a relatively peaceful federated ally of the Empire and a marauding threat.  Finally, in 401 under Alaric they were encouraged to enter the Western Empire where they eventually sacked Rome in 410.  In the final chapter of their wanderings they moved through northern Italy into Gaul where in 418 they reached a settlement with the Western Empire in which they were effectively granted control of the province of Aquitaine.  But the disruption of those years contributed to the growing chaos within the West.  As one indicator the devastation of Italy was so complete that the Emperor reduced taxes by more than 80% for several years in order to allow the province to recover.  It also contributed to the inability to respond to the crossing of the frozen Rhine by several tribes on December 31, 405 which eventually led to the loss of the provinces of Britain, Gaul and Spain.

(from mappery) 

The grip of Rome, particularly in the West was fraying in the late 4th century but the loss at Adrianople and the need of the Eastern Empire to deflect the Goths westward hastened its decline.