1) In the early centuries BC and AD, there were many migrations of Germanic tribes such as the Cherusci, Marcomanni, and Goths from northern Europe into Roman territory. 2) These migrations were often due to overpopulation, conflicts between tribes, or the desire for better land or Roman goods and protection from powerful tribes. 3) Notable events included the defeat of the Cimbri and Teutoni tribes by Marius in 102-101 BC, and the destruction of three Roman legions under Varus by Arminius and the Cherusci in the Teutoburg Forest in 9 AD.