the 2nd millennium BCE, the region was at the boundary between the Atlantic and Nordic horizons, split up in a northern and a southern region, roughly divided by the course of the Rhine. To the north emerged the Elp culture (1800-800 BCE), featuring an initial tumulus phase showing a close relationship to other Northern European tumulus groups (sharing pottery of low quality: Kümmerkeramik) and a subsequent smooth local transformation to the Urnfield culture (1200–800 BCE). The southern region became dominated by the Hilversum culture (1800–800 BCE), which apparently inherited the previous Barbed Wire Beaker cultural ties with Britain. From 800 BCE onward, the area was influenced by the Celtic Hallstatt culture. The current view in the Netherlands holds that subsequent Iron Age innovations did not involve substantial Celtic intrusions but featured a local development from Bronze Age culture. In the final centuries BCE, areas formerly occupied by the Elp culture emerge as the probably-Germanic Harpstedt culture west of the Germanic Jastorf culture, and the southern parts become assimilated to the Celtic La Tène culture, as is consistent with Julius Caesar's account of the Rhine forming the boundary between Celtic and Germanic tribes. Later, the Roman retreat resulted in the disappearance of imported products like ceramics and coins and a return to virtually-unchanged local Iron Age production methods. To the north, people continued to live in the same three-aisled farmhouse, and to the east, completely-new types of buildings arose. More to the south, in Belgium, archaeological results of the period point to immigration from the north. Roman era With the onset of historical records (Tacitus, 1st century), the area was generally called the border region between Celtic (Gaulish) and Germanic influence. Tribes located in the area include the Batavians, Belgae, Chatti, Hermunduri, Cheruscii, Salii, Sicambri, Tencteri and Usipetes or Usipii. Caesar took the course of the Rhine to be the boundary between Gauls and Germans (Germanic people) but also mentioned that a large part of the Belgae had ancestry from east of the Rhine and that one part were even known collectively as "Germani" (the so-called "Germani cisrhenani"). The Belgae were therefore considered Gaulish (the Usipetes Germanic etc.) because of their position with respect to the Rhine, and not in the modern linguistic sense of the terms. Some of those tribes would later join the Frankish confederation. See also Ambrones Archaeology of Northern Europe Dutch mythology Germanic substrate hypothesis Old Europe