The erdstall is type of tunnel prominently found scattered across Europe, predominantly in Bavaria, southeast Germany, and Austria. Thought to be crafted during the Medieval period, some theorists argue that these ancient subterranean structures date back to the Stone Age. The purpose of these mysterious tunnels remains a tantalizing enigma. Advocates for the Stone Age theory propose that these tunnels formed an extensive underground network stretching from Scotland to Turkey.
Erdstall Construction
The term 'erdstall' originates from German, signifying 'earth stable' or 'mining tunnel.' While there are various kinds of subterranean tunnels worldwide, the erdstalls have unique characteristics that set them apart. Typically, an erdstall network includes narrow, low tunnels, often oval-shaped and running either vertically or horizontally. These intriguing tunnels usually span between 20 and 50 meters. An especially distinctive feature is the 'schlupf' or 'slip out' – incredibly tight holes (around 40 cm in diameter) connecting tunnels at different levels.

Venturing into the Shadowy Depths of Erdstall
Currently, Europe is home to an estimated 2000 erdstalls, with Bavaria in Germany housing the lion's share of around 700. Its neighboring country, Austria, is not far behind with about 500 erdstalls. Countries like the UK and France also host these enigmatic underground passages.

The Cryptic Function of Erdstalls
The intended use of these erdstalls is still shrouded in profound mystery. In some local lore, the tunnels are believed to be the dwellings of mythical creatures like elves and gnomes, thought to have constructed them. Consequently, erdstalls often receive whimsical names reflecting these tales, like 'Schrazelloch' ('goblin hole') or 'Alraunenhöhle' ('mandrake cave'). Some believe they were secret escape routes linked to castles as some sagas suggest. However, this theory hits a snag as erdstalls typically have a single entry and exit point, rendering them unsuitable for such a purpose.

A Bold Assertion and its Hurdles
Others theorize these tunnels as hideouts, though their narrow dimensions and lack of airflow, due to the single entry-exit, would make it a rather inhospitable refuge. Some argue that the erdstalls were storage facilities, but the tight space and occasional waterlogging (especially in winters) deem it unlikely.

One of the most intriguing assertions suggests that these erdstalls were parts of an enormous subterranean network stretching from Scotland to Turkey. Further, they propose this network dates back to the Stone Age, dubbing it as an "ancient underground superhighway" for safe interregional travel. This theory, however, grapples with numerous issues, including the fact that the erdstalls aren't interconnected and are structurally dissimilar to the vast underground cities found in Turkey's Cappadocia regions.
Erdstalls remain a fascinating enigma. Despite the many theories and speculations about their origins and purpose, definitive answers are still elusive. Nevertheless, the study of these structures provides an intriguing glimpse into the past, and could potentially lead to new discoveries about the societies that built them. Their mysteries continue to captivate scholars, adventurers, and anyone with a curiosity for the unknown.
Top image: Erdstall entrance, Erdstall Ratgöbluckn, Austria ( CC BY-SA 3.0 )
By Wu Mingren
References
Daily Mail Reporter, 2011. Going underground: The massive European network of Stone Age tunnels that weaves from Scotland to Turkey. [Online]
Available at: http://www.dailymail.co.uk/sciencetech/article-2022322/The-massive-European-network-Stone-Age-tunnels-weaves-Scotland-Turkey.html
Grundhauser, E., 2015. We Still Don’t Know Why Medieval Europeans Built Their Mysterious ‘Erdstall’ Tunnels. [Online]
Available at: Going underground: The massive European network of Stone Age tunnels that weaves from Scotland to Turkey
Palma, B., 2016. Tunnel Trek. [Online]
Available at: http://www.snopes.com/stone-age-tunnels/
Schulz, M., 2011. Experts Baffled by Mysterious Underground Chambers. [Online]
Available at: http://www.spiegel.de/international/zeitgeist/hideouts-or-sacred-spaces-experts-baffled-by-mysterious-underground-chambers-a-775348.html
Tegün, T. M., 2016. Erdstall Tunnels Do Not Reach From Scotland to Turkey, Contrary to Rumor. [Online]
Available at: http://interestingengineering.com/the-tunnels-are-not-reaching-from-scotland-to-turkey/
Most of these have been dated to the Younger Dryas period when they were used as refuges from the cosmic bombardments that triggered the abrupt climate changes and mass fauna extinctions.
The Roman historian Tacitus writes in his Germania "They are likewise wont to scoop caves deep in the ground, and over them to lay great heaps of dung. Thither they retire for shelter in the winter, and thither convey their grain: for by such close places they mollify the rigorous and excessive cold." (from translation on gutenberg.org).