The clear-cut distinction between Germans east of the Rhine and Celts to its west was a political fiction of Julius Caesar, but one which was enshrined by his conquest of Gaul and the subsequent establishment of the Roman frontier along the Rhine.
Trade developed strongly, Roman traders often settling in Germanic lands. Tribes on the Roman borders soon developed a market economy, using Roman silver coins.
Beyond this contact zone, Roman jewellery, glassware and fine metal vessels enjoyed great popularity as prestige goods. They are found in the burials of chiefs who acted as middlemen facilitating the supply of materials like furs and amber from the north-east and also of slaves, usually prisoners of war.
Germanic groups further to the east in the 2nd century AD began putting pressure on the more settled regions to their south and west, setting in train incursions into Roman territory and eventually mass migrations. The Marcomannic War in AD 166-180 marked the first attempts by Rome to hold back the barbarian hordes. In the 3rd century more powerful confederacies of barbarians developed, attacking Roman lands to greater effect. As the empire weakened in the 4th century, it was gradually overrun by Germanic groups.