Quote from E. Cosack (2004): "Iron nails with a noticeably massive head occasionally appear in archaeological finds. Based on their technical characteristics, these are clearly fig nails. Such nails are required when using rim segments or cold-mounted rims. According to the evidence, fig nails must have come loose from wooden wagon wheels in many cases, especially since they are found in large numbers in the field during archaeological surveys. Mapping them could therefore provide another starting point for determining old traffic routes." Literature: Erhard Cosack, Iron nails with a massive head. A barely noticed archaeological group of finds. Die Kunde 55, 2004, 1–10.
Thank you very much - that would fit the location. Close to an old trade route on a rather rocky slope where the wheels must have reached their limits.