A Proto-Germanic population is believed to have emerged during the Nordic Bronze Age, which developed out of the Battle Axe culture in southern Scandinavia. During the Iron Age various Germanic tribes began a southward expansion at the expense of Celtic peoples, which led to centuries of sporadic violent conflict with ancient Rome. It is from Roman authors that the term "Germanic" originated. The decisive victory of Arminius at the Battle of the Teutoburg Forest in 9 CE is believed to have prevented the eventual Romanization of the Germanic peoples, and has therefore been considered a turning point in world history. [a] Germanic tribes settled the entire Roman frontier along the Rhine and the Danube, and some established close relations with the Romans, often serving as royal tutors and mercenaries, sometimes even rising to the highest offices in the Roman military. Meanwhile, Germanic tribes expanded into Eastern Europe, where the Goths subdued the local Iranian nomads and came to dominate the Pontic Steppe, simultaneously launching sea expeditions into the Balkans and Anatolia as far as Cyprus.