During the time of Roman expansion in Europe, the Romans encountered many Germanic tribes on the other side of the Rhine and Danube rivers.
The German people were a constant threat to the Empire since the first appearance of the Cimbri and Teutones at the end of the second century BC. Julius Caesar encountered them in his campaign in Gaul, in mid 1st century BC. In his memoir, called Gallic Wars, Caesar was able to distinguish the German from the Celts.
The origin of the German people was obscure, but it is believed that they were originally from Scandinavia, before migrating to northern Germany and the Baltic. More Germanic tribes

began migrating south, placing continuous stress on Roman defence frontiers.
A Roman historian named Tacitus, (fl. AD 100), who wrote Germania, provided some details of the German society culture and religion. Other writers including Strabo, Jordanes, and Procopius.
The continuous invasions and migrations on the Roman frontiers had caused instability and finally the collapse of the Roman Empire in the west.
Most of the Germanic religions and myths unfortunately vanished.

see the list of germanic tribes