A New Class of Subterranean Dry-Stone Structures: River-Pebble Walls in the Ravne Tunnel Complex, Bosnia-Herzegovina

Dry-stone construction is a globally recognized architectural technique dating back to the Neolithic period and earlier. While surface-level dry-stone features have been extensively studied throughout the Mediterranean and Central Europe, subterranean dry-stone structures built entirely from river pebbles are exceptionally rare and largely undocumented. Over the past two decades, systematic excavation and multidisciplinary analysis in the Visoko Valley of Bosnia-Herzegovina have revealed an extensive network of underground tunnels known as the Ravne Tunnel Complex. Within this labyrinthine system—comprising Ravne, Ravne 3, Ravne 4, and Ravne 6—more than sixty dry-stone walls have been documented as of 2025. These structures were constructed without mortar, often to seal side passages or stabilize cavities, and in some cases stretch several meters in length and height. This article presents the first formal typological, geological, and archaeological study of these walls. It integrates stratigraphic observations, radiometric dating (including both U-Th and radiocarbon methods), and detailed mapping. Our findings establish that the Ravne dry-stone walls represent a previously undocumented class of subterranean construction, bearing no parallel in currently published Balkan or global contexts. Radiocarbon dating of charred material found near one of the longest walls indicates human activity in the 4th century CE, confirming a phase of historical reuse. The data presented here offer robust evidence that the Ravne Tunnel Complex features deliberate, anthropogenic subterranean architecture, with significant implications for the understanding of pre-industrial construction practices and regional underground heritage.