The Germanic-speaking peoples speak an Indo-European language. The leading theory for the origin of Germanic languages, suggested by archaeological and genetic evidence, postulates a diffusion of Indo-European languages from the Pontic–Caspian steppe towards Northern Europe during the third millennium BCE, via linguistic contacts and migrations from the Corded Ware culture towards modern-day Denmark, resulting in cultural mixing with the earlier Funnelbeaker culture. The subsequent culture of the Nordic Bronze Age (c. 1700-c. 600 BCE) shows definite cultural and population continuities with later Germanic peoples, and is often supposed to have been the culture in which the Germanic Parent Language, the predecessor of the Proto-Germanic language, developed.
Generally, scholars agree that it is possible to speak of Germanic-speaking peoples after 500 BCE, although the first attestation of the name “Germani” is not until much later. Between around 500 BCE and the beginning of the Common Era, archeological and linguistic evidence suggest that the Urheimat (‘original homeland’) of the Proto-Germanic language, the ancestral idiom of all attested Germanic dialects, was primarily situated in the southern Jutland peninsula, from which Proto-Germanic speakers migrated towards bordering parts of Germany and along the sea-shores of the Baltic and the North Sea, an area corresponding to the extent of the late Jastorf culture.
According to some authors the Bastarnae or Peucini were the first Germani to be encountered by the Greco-Roman world and thus to be mentioned in historical records. They appear in historical sources going back as far as the 3rd century BCE through the 4th century CE. Another eastern people known from about 200 BCE, and sometimes believed to be Germanic-speaking, are the Sciri, who are recorded threatening the city of Olbia on the Black Sea. Late in the 2nd century BCE, Roman and Greek sources recount the migrations of the Cimbri, Teutones and Ambrones whom Caesar later classified as Germanic. The movements of these groups through parts of Gaul, Italy and Hispania resulted in the Cimbrian War (113–101 BCE) against the Romans, in which the Teutons and Cimbri were victorious over several Roman armies but were ultimately defeated.