These migrations were in no way nomadic; they were the gradual expansions of a land-hungry peasantry. Tribes did not always migrate en masse. Usually, because of the loose political structure, groups remained in the original homelands or settled down at points along the migration route. In the course of time, many tribes were depleted and scattered. On the other hand, different tribal groups would sometimes unite before migrating or would take up other wanderers en route. The migrations required skilled leadership, and this promoted the social and political elevation of a noble and kingly class.
In 102 bce the Teutoni were totally defeated by the Romans, who in the following year destroyed the army of the Cimbri. The Swabian tribes, however, moved steadily through central and southern Germany, and the Celts were compelled to retreat to Gaul. When the Germans under Ariovistus crossed the upper Rhine, Julius Caesar arrested their advance and initiated the Roman countermovement with his victory in the Sundgau (58 bce). Under the emperor Augustus, Roman rule was carried as far as the Rhine and the Danube. On the far side of these rivers, the Germans were pushed back only in the small area contained within the Germano-Raetian limes (fortified frontier) from about 70 ce.
The pressure of population was soon evident once more among the German peoples. Tribes that had left Scandinavia earlier (Rugii, Goths, Gepidae, Vandals, Burgundians, and others) pressed on from the lower Vistula and Oder rivers (150 ce onward). The unrest spread to other tribes, and the resulting wars between the Romans and the Marcomanni (166–180) threatened Italy itself. The successful campaigns of Marcus Aurelius resulted in the acquisition by Rome of the provinces of Marcomannia and Sarmatia, but after his death these had to be abandoned and the movement of the Germanic peoples continued. Soon the Alemanni, pushing up the Main River, reached the upper German limes.
To the east the Goths had reached the Black Sea about 200 ce. Year after year Goths and others, either crossing the lower Danube or traveling by sea, penetrated into the Balkan Peninsula and Anatolia as far as Cyprus on plundering expeditions. Only with the Roman victory at Naissus (269) was their advance finally checked. Enriched with booty and constituted imperial mercenaries in return for the payment of a yearly tribute, they became a settled population. The Romans, however, surrendered Dacia beyond the Danube.
In 258 the Alemanni and the Franks broke through the lines and settled on the right bank of the Rhine, continuously infiltrating thereafter toward Gaul and Italy. Everywhere within the empire, towns were fortified, even Rome itself. Franks and Saxons ravaged the coasts of northern Gaul and Britain, and for the next three centuries incursions by Germanic peoples were the scourge of the Western Empire. Nevertheless, it was only with German help that the empire was able to survive as long as it did. The Roman army received an ever-growing number of recruits from the German tribes, which also provided settlers for the land. The Germans soon proved themselves capable of holding the highest ranks in the army. Tribute money to the tribes, pay to individual soldiers, and booty all brought wealth to the Germans, which in turn gave warrior lords the means with which to maintain large followings of retainers.
In the West, however, among the Alemanni and Franks, the beginnings of political union into larger groups did not go beyond loose associations. Only in the East did the Gothic kingdom gather many tribes under a single leadership. Above all, the development of the eastern Germans was stimulated by their undisturbed contact with the frontiers of the ancient world. Their economy, however, was still unable to support the needs of a steadily growing population, and pressure from overpopulation resulted in further incursions into the Roman Empire. The imperial reforms of Diocletian and Constantine the Great brought a period of improvement. The usurpation of the imperial title by a Frankish general in 356 let loose a storm along the length of the Rhine and subsequently on the Danube, but the frontiers were restored by the forces of the emperors Julian and Valentinian I, who repelled attacks by both the Franks and the Alemanni.
At that time, a new force appeared. In 375 the Huns from Central Asia first attacked the Ostrogoths—an event that provoked serious disturbances among the eastern Germans. The Huns remained in the background, gradually subjugating many Germanic and other tribes. The terrified Goths and related tribes burst through the Danube frontier into the Roman Empire, and the Balkans became once again a battlefield for German armies. After the crushing defeat of the Romans at Adrianople (378), the empire was no longer in a position to drive all its enemies from its territories. Tribes that could no longer be expelled were settled within the empire as “allies” ( foederati). They received subsidies and in return supplied troops. The Germanization of the empire progressed, that of the army being nearly completed. None of the tribes, however, that had broken into the Balkans settled there. After the division of the empire in 395, the emperors at Constantinople did all in their power to drive the Germanic tribes away from the vicinity of the capital toward the Western Empire.
From the beginning of the 5th century, the Western Empire was the scene of numerous further migrations. The Visigoths broke out of the Balkans into Italy and in 410 temporarily occupied Rome. In 406–407, Germanic and other tribes (Vandals, Alani, Suebi, and Burgundians) from Silesia and even farther east crossed the Rhine in their flight from the Huns and penetrated as far as Spain. The Vandals subsequently crossed to Africa and set up at Carthage the first independent German state on Roman soil. In the Battle of the Catalaunian Plains (451), the Roman commander Aëtius, with German support, defeated Attila, who had united his Huns with some other Germans in a vigorous westward push. The Balkans suffered a third period of terrible raids from the eastern Germans; and Jutes, Angles, and Saxons from the Jutland Peninsula crossed over to Britain. The Franks and the Alemanni finally established themselves on the far side of the Rhine, the Burgundians extended along the Rhône valley, and the Visigoths took possession of nearly all of Spain. In 476 the Germanic soldiery proclaimed Odoacer, a barbarian general, as king of Italy, and, when Odoacer deposed the emperor Romulus Augustulus at Ravenna, the empire in the West was at an end. In the East, imperial rule remained a reality, and Constantinople, also called “New Rome,” survived many sieges until its fall in 1453. In comparison, “Old Rome” declined into an episcopal centre, losing many of its imperial characteristics. Hermann Aubin The Editors of Encyclopaedia Britannica The reconfiguration of the empire
By the end of the 5th century, however, most of the non-Roman peoples settled in the West were adopting Roman customs and Christian belief. Intermarriage with established Roman families, the assumption of imperial titles, and, finally, conversion assisted a process of acculturation among their leaders, for instance, in the case of Clovis, the Frank. Theodoric the Ostrogoth established an impressive “sub-Roman” kingdom based on Ravenna, where public buildings and churches served by an Arian clergy competed with imperial monuments. Increased Roman influence can also be seen in the law codes promulgated by the Visigoths Euric (late 5th century) and Alaric II (the Breviary of 506) and the Burgundians, Bavarians, Ostrogoths, and Franks (Lex Salica, 507–511). Christianity often provided the medium for incorporation into old imperial structures. While the Goths were still in the Danube basin, they had embraced Arian Christianity (which denied that the Son was of the same substance as the Father), and their first bishop, Ulfilas, translated the Bible into Gothic. Given its heretical nature, this religious literature in a written vernacular could not survive, and, with conversion to orthodox (“catholic”) Christianity, the barbarian languages gradually gave way to Latin.