The Germanic migrations changed the course of Western history, as the invaders replaced or transformed the Roman empire. The invasion of the Kimbrian and Teutonic tribes from overpopulated, hungry Jutland (peninsular Denmark) in 120 BC involved some 100,000 people, plundering through Germany and absorbing other destitute Germanic populations. Next they followed the Danube plain south to Thrace and west to Italy, even overcoming a Roman consul's army at Noreia (in Carinthia) in 113 BC, the Furor Teutonicus. Biometric reconstruction confirms they were a head taller then Romans. Ten years they plundered Gaul and Spain, until Roman general Marius exterminated their hordes in 101 BC.
The Goths -including Gepides- started wandering from Scandinavia's Ostsee coast, to Poland, initially slow and fairly peaceful, then fast to the Danube. In 9 BC a Germanic alliance lead by the Cherusk tribe's honorary hostage, Arminius, defeated Roman invasion governor Varrus's three legions in Germania, ending the dream of turning it into another Roman province.
In 376 AD, the invasion of Attila's Huns started the major Germanic migration. Then West Goths invaded the Roman empire's heart land, Italy, only to be forces further west, ending up as rulers of Iberia. The Ostrogoths however started a complex migration, ending up as rulers of an Italian kingdom.
In 507, the Frankish invasion of the Empire, mainly flooding Gaul started the final, fatal round of Germanic immigration into the remainder of the West Roman empire. The West Goths and Suevi retreated south, to Iberia, until the Muslim flood.