The Germanic tribes lived in relatively peaceful coexistence with their southern neighbors until the latter part of the First Century and the beginning of the Second Century AD. Around that time they began to move southward.
There were a number of reasons for the mass migration, but one in particular outweighed the others. The food supply was dwindling. Through the latter part of the Mesolithic Age, the entire Neolithic Age and into the Bronze Age, the climate of the region bordering the North Sea had been very beneficial to the growing of food crops. But as the Bronze Age waned, the climate began to change to a cold, damp one in general. The winters were becoming harsher and the summers were not long enough to bear sufficient crops. To top it off, a period of geothermal warming was causing the ocean levels to rise. Large areas of the Baltic and North seacoasts were becoming flooded.
Individual Germanic tribes began to move southward in search of new homelands. The Basternae reached the Black Sea region around 230 BC. They survived there for over two hundred years, eventually being forced into conflict with the expanding Roman Empire circa 29 BC. The incursion of the Goths into the region around 170 AD resulted in the virtual elimination of the Basternae as a tribe.
The Vandals are believed to have originated in North Jutland. They moved southward into the region of the Vistula in present-day Poland. Tribal wars decimated the Vandals, but some of them traveled into Gaul, where they would grow in numbers.
Two tribes left the region of North Jutland around 120 BC: the Cimbri and the Teutones. They followed the old amber trade route up the Elbe River into Bohemia where they encountered and were repressed by the Celtic Boii tribe. They then traveled through Silesia, Moravia and Hungary and reached the Danube and the Eastern Alps in 113 BC. They moved on into Gaul and remained there for eight years. During their sojourn in Gaul, the Cimbri and Teutones defeated five Roman armies. But their luck ran out in 102 BC when a Roman army under General Marius defeated the Teutones at Aquae Sextae in southern Gaul. In 102 BC Marius defeated the Cimbri in northern Italy. The victories encouraged the Romans to extend their empire into Gaul. They began to make alliances with certain individual Germanic tribes, such as the Saxons. Those Germanic tribes were incorporated as foederati, or confederated allies, into the Roman Empire, which explains how the Empire was able to expand at the rate it did.
The first appearance of extended German tribes in written history were the Quadi and the Marcomanni, who invaded the region along the Danube in the period from 166 to 180 A.D. The two tribes both arose in the region of present-day Bohemia. The existence of the Quadi and the Marcomanni as unified Germanic tribes was brought to an end by the Romans against whose Empire their invasion was directed. The majority of the men were forced into service for the Roman army and sent to Britain to fight there for the Roman Empire.
The next, and more extensive invasion of the Roman Empire’s borderlands, came from another Germanic tribe: the Goths. The Goths launched their invasion from Gotland, moving down the Dniester River toward Dacia. A concerted effort was made by the Goths to capture the Dacian region (i.e. modern Roumania) between 254 and 268 A.D. In 260 AD the Goths divided into two factions: the Ostragoths (i.e. the Eastern Goths) and the Visigoths (i.e. the Western Goths) due to disagreements between two leading families. A Gothic fleet invaded the Aegean in 268 and plundered the cities of Greece and Asia Minor. The Mediterranean invasion was brought to a halt when the Goths attacked Thessalonica. The Roman army under Claudius II encountered the Gothic army at Naissus and was victorious in repelling the invaders.
The defeat at Naissus did not end the Gothic invasion. They retained possession of the region of Dacia. By the year 275, the Romans had evacuated Dacia and the Goths settled down in peaceful coexistence with their Roman neighbors. It was out of that period of peace that the Goths began to accept certain of the tenets of the Christian religion. The Ostragoths were virtually destroyed as a tribe by the Hun invasion of the Fourth Century AD from out of the Central Asian steppes. The Visigoths, on the other hand moved southwestward into Gaul and Spain and eventually became foederati of the Roman Empire, serving with the Romans against the Germanic Vandals in 451.
An impact of the Gothic invasion of Dacia, more important than the effect it had upon the Roman Empire, was that other Germanic tribes were pushed westward. The unrest caused by the displacement of the smaller Germanic tribes spurred the formation of extended tribes or confederacies such as the Alemanni, Franks, Bavarians, Saxons, Thuringians and the Frisians.
The Alemanni originated in the region along the Neckar River and as they got squeezed in by the Goths, they in turn moved into the Black Forest. They took control of the village of Aqua Aureliensis (i.e. Baden-Baden) along the Danube. They attempted an invasion of the region known as Gaul, but were prevented. Crossing the Alps along the northern border of Italy, the Alemanni confronted the Romans under Claudius II at Lake Garda, but were repelled there also. In the year 270, the Po Valley was the next region into which the Alemanni invaded. The Roman army under Aurelian again repulsed the Germanic aggressors. The Alemanni once more attacked Gaul in 285, but were repulsed by Emporer Diocletian. Continual defeats finally convinced the Alemanni that they could not triumph over the might of the Roman Empire. They eventually gave up the fight and settled along the upper Rhine.
The large extended tribe called the Franks became noticeable as a separate and distinct people in the Second Century, being mentioned in historical writings for the first time around the year 256 AD. In A.D. 256, the Franks along the Lower Rhine started to move southward in a major migratory push toward the Mediterranean. Their move into Gaul and northern Spain was, no doubt, induced by the pushing into their homelands by the Saxons. In 273 the Roman army under Aurelian fought the Franks and took a great number of them into captivity. The captured Franks were sent to Britain, Thrace and Asia Minor as colonists of the Roman Empire.