In the course of the Iron Age which followed (from about 800 BC), the Celts became the first identifiable tribe in the region. They built a chain of hillforts in northern Franconia as a defensive line against the Germanii who were pressing in from the north. On the Staffelberg they built a mighty settlement, which was mentioned by Ptolemy under the name of oppidum Menosgada. Another was built on the Gleichberge: the largest surviving oppidum in Central Germany, the Steinsburg. With the accelerating expansion of Rome in the first century BC and the simultaneous advance of the Elbe Germanic tribes from the north, Celtic culture began to decline. A Germanic cemetery from this period, which was used for a long time, is located in what is now Altendorf in the county of Bamberg.