An alternative interpretation of the ramparts of the defensive settlement of the Lusatian culture in Biskupin in the light of analyses of source materials and expert reports

Abstract

Biskupin, which was interpreted on the basis of cultural-historical archaeology by J. Kostrzewski and Z. Rajewski, remained an “explained” object for many years. The interpretation of knowledge about Biskupin contained therein was a reference point for many synthesizing studies and analyses, in which this object was most often presented as the pinnacle of the local community's achievement in the early Iron Age in terms of internal layout and advanced construction techniques. In 2000, Andrzej Mierzwiński proposed an alternative, hydrotechnical reinterpretation of the ramparts and gate in this defensive settlement. He pointed out that the existence of the ramparts is assumed and should be the subject of source analyses. According to him, climate change, which caused an increase in the water level in Lake Biskupin, was the reason for the construction of a low dam around the settlement. In his subjective opinion, a high rampart would be an unstable structure because its walls would not withstand the pressure exerted on the walls by the filling of the rampart boxes. An additional argument supporting this thesis was the instability of the building's soil (peat). An additional argument supporting this thesis was the unstable soil (peat). According to Andrzej Mierzwiński, adding an additional row of boxes to the outer row was evidence of attempts to protect the interior of the settlement against flooding during the transgression of Lake Biskupińskie. He also reinterpreted the gate, the remains of which in the form of two rows of palisades and the road between them were, according to him, the remains of the land part of the bridge (bridge abutment).

The proposed reinterpretation of the ramparts and gate should be interpreted as an attempt to break the current interpretation of Biskupin. The basis of this perspective was the belief that this object had already been explained and that all statements about it did not refer to it, but to an interpretation repeated many times, which over time became obvious.

Verification of Andrzej Mierzwiński's hypothesis also allows for a broader assessment of the influence of Lake Biskupin's waters on the settlement structures of the early Iron Age. The location and topography of the terrain where the settlement was established meant that this area, and in particular the lowest part of the site in the north-west (approximately 0.50 m above the average water level at the turn of the Bronze Age and the early Iron Age), was particularly exposed to the influence of Lake Biskupin. The analysis of available source materials (geological cross-sections, drawings, photographs, scientific expertise etc.) indicates that the transgressions of Lake Biskupin in the early Iron Age were cyclical and did not always occur during the period of use of the settlement in Biskupin. The flood risk is confirmed by alluvial layers found in the northern, western and central parts of the settlement. Certain indications, such as the construction details of the buildings, the raising of the level of floor and street, may indicate that during the construction of the buildings and probably the oldest rampart (W1) in the northern part of the settlement, a slight transgression of Lake Biskupińskie took place. The effects of this hypothetical flood could have resulted in the abandonment of work on the construction of the W1 rampart, the remains of which were found only in the north-east, and the commencement of construction of the older rampart (W2) at a greater distance from the lake. The usable level in some buildings and a section of the circular street was also raised. Due to a fire of the rampart from the older stage of the settlement (W2), and then due to the denudation of the material filling the rampart boxes, during the transgression of Lake Biskupińskie, the interior of the settlement was flooded. The site area in the lowest part in the north was covered with a layer of sediments of considerable thickness. The accumulation of flood materials contributed to the elevation of the area of ​​the settlement in its lowest part by approximately 0.5 m. During the period of the following regression of Lake Biskupin, the area of ​​the site, the level of which was raised due to the accumulation of alluvia, created favorable conditions for the construction of a younger defensive settlement. During the construction of the settlement in the younger stage, Lake Biskupińskie did not pose a flood risk, as evidenced by the break in the rampart (W3) in the northern part of the settlement. The last transgression, which occurred after the destruction of the younger rampart (W3) caused by fire, covered an area comparable to the previous flooding of the interior of the settlement (northern, western and central parts of the settlement). The third and final stage of settlement from the Early Iron Age (probably at the end of  HaC) represents open settlement. Construction of buildings was preceded by earthworks, which involved covering the ruins of the defensive settlement with material from the filling of the rampart W3. These actions, which could have been initiated for reasons other than adaptation to the increased level of Lake Biskupin, averted the potential flood risk. In the layers identified with the last stage of settlement of the Early Iron Age, no alluvial deposits were found.

The construction of the ramparts, and in particular the rampart of the younger stage of the defensive settlement (W3), did not fit into the strategy aimed at counteracting transgression. This is evidenced by many factors, including the existence of a break in the W3 rampart, in the part of the settlement that was most exposed to the impact of Lake Biskupińskie. The structure and properties of materials used to fill the rampart W2 also indicate the intention to protect its upper part against atmospheric precipitation and to ensure the outflow of water from the interior of the rampart to the ground.

Numerical analysis of the model based on the parameters of the rampart W2 showed that this structure, filled with loose material, without supporting posts placed along the outer walls, meets the requirements of overall stability at a maximum height of 13.7 m. However, the less technically advanced construction of the rampart W3 required the use of posts to prevent the box logs from sliding apart.

The unfavorable properties of the subsoil (peat) were compensated for by distributing the weight of the ramparts over a larger surface area. The susceptibility of the rampart subsoil to deformation caused by the weight of these structures was balanced by soil compaction and the pressure exerted by the weight of the structures erected in its immediate vicinity (breakwater, ring road), some of which were additionally weighted with piles of stones.

The community occupying the defensive settlement in Biskupin reacted to the effects of the impact of Lake Biskupin through strictly adaptive actions (raising the level of streets and floors, modifying the structure of houses, building ramparts at a greater distance from Lake Biskupin), and not by counteracting increased water levels (building of dams).

The reinterpretation of the gate, like the alternative function of the ramparts, reflects a focus on the preconceived hydrotechnical function of these structures. This narrowing of the interpretation diverted the narrative from attempts to address the multifaceted interpretations of the structures within the gate, which were developed through cultural-historical archaeology and supported by engineering knowledge. In Andrzej Mierzwiński's approach, the hydrotechnical function of the ramparts was the starting point, to be proven by speculations guided by his own understanding. The lack of references to source materials from Biskupin and the focus on the hydrotechnical function of the ramparts did not provide the impetus for further exploration of solutions, but rather a critique of the prevailing narrative.