Hallstatt culture
In the centuries just before the arrival of the Romans, northern areas formerly occupied by the Elp culture emerged as the probably Germanic Harpstedt culture while the southern parts were influenced by the Hallstatt culture and assimilated into the Celtic La Tène culture. The contemporary southern and western migration of Germanic groups and the northern expansion of the Hallstatt culture drew these peoples into each other's sphere of influence. This is consistent with Caesar's account of the Rhine forming the boundary between Celtic and Germanic tribes.