Heidengraben is the name given to the remains of a large Celtic fortified settlement (oppidum) dating to the Iron Age. The settlement was in use from about the late 2nd century BC to the early 1st century BC. By surface area, Heidengraben is the largest oppidum in all of mainland Europe.
The outer fortifications delineate an area of over 1,700 hectares, making this oppidum the largest known in mainland Europe. The 2.5 km long walls make strategic use of the escarpment to create this large area surrounded either by wall or steep bluff. The walls cut off the inner area from the rest of the plateau and also divide it from three sections that are hard to fortify or oversee. In front of the wall was a moat. The rampart, in parts still about 3 m high, has eight gates. One of them, with a 35 m long entry way, is one of the largest and best-preserved of its kind.
The inner fortification, to the south-west, named Elsachstadt, likely marking the core of the Celtic settlement, covers around 153 hectares. It is surrounded by part of the outer wall and another inner rampart with a double moat and three gates. Not much is known about the internal settlement structures, however, as the buildings were made of wood and the area has been subject to erosion and been used for agriculture for centuries. Only the Elsachstadt was apparently also fortified in the direction of the escarpment. Overall, there are around half a dozen wall segments visible today, varying in length from a few hundred to over 1,000 m.
Stone artefacts indicate that humans frequented the area from the Ice Age to the 3rd millennium BC. There is some evidence that the area was inhabited since the Neolithic period. However, findings make it more likely that it was not used for settlement by Neolithic farmers but for gaining access to Hornstein. There is just one grave dating to the middle Bronze Age (1600-1300 BC) but several graves nearby date to the late Bronze Age and some burial mounds (with wooden chambers) are from the early Iron Age.
The actual Heidengraben was likely created in the late La Tène period (late 2nd century BC to early 1st century BC). However, in the period of 250 to 150 BC the area seems to have been once again unpopulated. Archaeological findings indicate the presence of a simple agricultural population as well as specialized artisans (metal working, glass production). In addition, a large number of shards from Roman amphorae dating to 130 to 90 BC indicate that a significant amount of Roman wine was imported. This implies the existence of a rich elite that could afford these luxury items. No evidence of a burial site dating to the oppidum period has been discovered, but the earlier necropolis seems to have been used as a cult site and possibly for burial rituals.
Around 85 AD the Romans occupied the Swabian Jura and there were some farms or mansiones in the area. The Romans left c. 260 AD. The next signs of inhabitants date to the 7th century, when the area was settled by Alemanni.
In the Middle Ages the area was only sparsely inhabited but some castles were constructed nearby like Hohenneuffen Castle (early 12th century) or Burg Hofen east of Grabenstein. The purpose of a medieval fortification surrounding 55 hectares to the north of Heidengraben (known as Bassgeige) is still unknown. It incorporates parts of a Celtic wall but was extended in late medieval times. Several similar structures nearby (Brucker Fels and Beurener Fels) also served an unknown purpose.
Much of the area is accessible to the public and there is an archaeological hiking trail called Achsnagelweg. In Grabenstetten, there is a museum (Keltenmuseum). Other findings can be viewed at the museum of the University of Tübingen.
References:
