Even before it was evacuated, Trajan's Dacia was effectively lost, because, as early as 248, attacks by the Goths and their allies were beginning to sever from the empire a territory that thrust deep into Barbaricum. Dacia's extinction is almost unfathomable, for it came about as a consequence of events that occurred south of the Danube, in today's Balkan peninsula.

The prelude to Dacia's disappearance was the arrival of the Goths and their allies on the coast of the Black Sea ca. 235; in the process, they ravaged the Greek-Roman settlements — including the walled stronghold of Deraclea — at the mouths of the Dniester and Bug rivers. In 238, they broke through the Romans' defensive line on the lower Danube and sacked the city of Histrus (Histria) in Scythia Minor (today's Dobrudja).

Events took a disastrous turn when, in 248, the allied Goths, Carpi, and Taifal launched an offensive against Moesia. Within a year, they devastated the right bank of the lower Danube, reaching Iatrus (Arčar), Novae (Svistov), and — as attested by a coin hoard, dating from 250 and discovered at Sofronievo in 1970 — the valley of the Augusta (Ogosta) River, which flows northward into the lower Danube, in present-day northwestern Bulgaria. They thus began to threaten Dacia's road links, north of the Danube. Although Emperor Decius checked their advance on this front in 250, when the enemy turned southward, he could not prevent them from seizing Philippopolis (Plovdiv), the first major city to fall to the enemy. Its inhabitants were put to the sword or taken prisoner. The following year, Moesia's defences collapsed. For the first time, in the {1-140.} great battle fought against the Goths near Abrittus (May or June 251), a Roman emperor, Traianus Decius, was killed in action; another casualty was his son, Herennius Etruscus.

Following this victory, the enemy pressed forward to Thessaloniki. The Romans had to defend the pass at Thermopylae and fortify Athens (254). By 257–58 the Goths had captured Olbia and Tyras, two ancient Greek cities on the Black Sea; thereafter, the towns' industries crafted weapons for the Goths, and their ships became the Goths' armed fleet. As early as 258, the Gothic-Herulic fleet ravaged towns on the coasts of the Black Sea and Propontis (Sea of Marmara). The Aegean coast suffered similar attacks a few years later; hallowed Ilion (Troy) was put to the torch, as was (in 262) Ephesus, famous for its temple of Artemis. In 264, the Goths reached Galatia and Cappadocia, and Gothic pirates landed on Cyprus and Crete. In the process, the Goths seized enormous booty and took thousands into captivity. Among those captured were the maternal ancestors of Bishop Vulfila, the Goths' 'apostle'.

Dacia's fate was sealed when, in 268–69, the Goths launched another offensive in the Balkans. They reached Greece, sacking Athens, Corinth, and Sparta, then, loaded with booty, marched northward. Although in 269, at Naissus (Niš), the Goths suffered a severe defeat at the hands Emperor Claudius II 'Gothicus', they kept up the pressure on the Romans' Danube line and, in 270, once again raided Dobrudja. By then, the Romans had withdrawn their forces from Dacia Superior, where the towns did not hold out for long against the invaders. Emperor Aurelian had little prospect of retaking the area north of the Carpathians; instead, he proceeded to evacuate troops and civilians from Dacia Inferior, known at the time as Dacia Transdanuviana, and today as the eastern Temesköz and Wallachia.

No details survive concerning the operations by which Carpi, Goths, Taifals, Gepids, and Vandals smashed the peripheral and internal defences of the Transylvanian part of Dacia, but the {1-141.} process must have begun around the end of Gordianus III's reign (238–244), when the province's inhabitants buried their coins, notably at Potaissa-Torda, Cege, Domáld, and Lozsád. Another wave of panic must have struck shortly thereafter, from Mezőbánd to Kemenceszék, in Krassó-Severin county; the latest coins found in these areas were minted under Philippus II (247–249). There is evidence of coins still circulated, at a reduced rate, during the reigns of Philippus Arabs I (244–249) and Decius (249–251); then the circulation virtually ceased. Between 268 and 271, the occupation of Dacia was completed with the capture of towns and a few inhabited forts, such as Sóvárad. Transylvania and the Romanian plain become Gutthiuda or, as the Romans called it, Gothia/ Gotia — 'the Goths' country'. Oltenia, the area between the Olt and Danube rivers, was occupied by the Goths' allies, the Taifals, after 270.

Having conquered Transylvania, the formerly united Gothic tribes divided into two groups. The Ostrogoths (austro = 'bright, shining, brilliant') settled east of the Dniester, as far as the Crimean Peninsula, while the Visigoths (vezu/vizu = 'good, brave, valiant') established themselves west of the Dniester. (The subsequent interpretation of the names as signifying eastern and western Goths is linguistically incorrect, even though it happens to reflect the pattern of settlement.) However, between 271 and 376, the two groups of Goths identified themselves by different names, which arose from their environment. Those living in the east were called Grutungi or Greutungi — meaning 'lowlanders' — while those settled on the fringes of Transylvania and the southeastern Carpathians were known as Tervingi — 'forest people'. The latter must have acquired the name only after they settled in the Transylvanian-Carpathian region; it first appears in contemporary records in 291 ('Tervingi, pars alia Gothorum, adiuncta manu Taifalorum adversum Vandalos Gepidesque concurrant'[1]1. Panegyrici Latini III (XI) 17.). Around that time, or a little earlier, the Tervingi and the Taifals had joined forces to repel Gepids and Vandals intent on seizing a share of formerly Roman Dacia.

{1-142.} The battles were waged on the territory of the former province, somewhere in the Szamos valley, for it is recorded that the Gepids and Taifals (led by Fastida) confronted the Tervingi-Taifal coalition (led by King Ostrogotha) near a town. Since there is no evidence of a Gothic settlement in the Gutthiuda larger than a village or fortified position, the reference in 'ad oppidum Galtis, iuxta quod currit fluvios Auha'[2]2. Jordanes, Getica 99. must be to a onetime Roman town. Notwithstanding much uninformed speculation, the identity of this town on the river 'Auha' (from the Gothic ahwa, meaning 'water, river') is unknown, and probably destined to remain so, for it is unlikely that new written sources will be discovered, and the original source (Ablabius' 'Origo Gothica) drew its information from legends in the Gothic language.

Up to 328, the main events of Visigothic-Roman history unfolded along the ripa gotica — 'the Gothic riverbank' on the lower Danube. This does not, however, put into question the existence of Goth settlements in Transylvania, notably in the Maros valley. In fact, during the reign of King Ariarik, the Goths of Transylvania advanced along the Maros in an attempt to drive the Sarmatians off the lowlands of the Temesköz. The Sarmatians turned for assistance to Constantine the Great, who sent a large Roman force led by his son, the future Constantius II. This army won a formidable victory over the Goths in Sarmatia on 18 February 332. Thousands of Goth warriors were captured, and an onerous and humiliating peace was imposed upon the Goth kings. This was probably the occasion when Vidigoia, 'the bravest Goth', was killed as a result of 'Sarmatian trickery'. The place where he fell, and perhaps his grave as well, were long remembered; in 449, when Priscos crossed the Temesköz on his way to Attila's 'capital', the 'ordu', his escort could still lead him to the historic spot.

However, the Goths did not give up the control of the Transylvanian entrance of the Maros valley. When, around 335, the army of the Vandal King Visumar tried to settle there, a force of {1-143.} Transylvanian Goths under the command of Geberik, son of Ovida, drove them away.

In 364 and 369, Emperor Valens launched attacks against the Tervingi from the lower Danube, but to little effect, for the iudex Athanarik withdrew not only his troops but also the rest of his people, partly to the wetlands of the Danube Delta, partly to the 'Serrorum montes' (the Southern Carpathians), and, of course, to Southern Transylvania.

In the summer of 376, the Huns, after defeating the Greutungi, proceeded to crush the Tervingi Goths. They outflanked Athanarik's advance guard (commanded by Munderic), swam across the Dniester — which the Goths considered impassable — at nighttime, and, as dawn rose, they fell upon the Goth camp guarding the ford on the river. (Centuries later, the same brilliant 'nomad' tactic was employed by the Hungarians at Pozsony and by the Mongols at Muhi.) The result was a panic of a kind never recorded in world history until then. That autumn, the Visigoth tribes, commanded by Alavivus and Fritigern, crossed the Danube to seek refuge on Roman territory, while, following a succession of defeats, Athanarik and his retinue withdrew into the mountains. It is not clear whether the area known to the Goths as Kaukalanda (in Gothic: 'the country of mountains') includes all of the Carpathian highlands known to them, or only part of the highlands ('Caucalandensis locus'); but in both cases the name refers to Transylvania.

In the late autumn of 380 or 381, Athanarik and his escort were routed by an enemy force that is not identified in recorded history, but which, as will be seen, probably consisted of Gepids. Despite a 'vow' that he had proudly evoked as late as 369, Athanarik fled across the Danube to Roman territory; he reached Constantinople on 11 January 381, and died a few days later. Thus ended the rule of the 'woodland' Goths and the first 'post-Roman' phase of Transylvania's history.