Strongholds and landslides - examples of the use of landslides as natural elements of former defensive structures (Racibórz-Oświęcim basin).
Today landslides are considered only negative phenomena - they pose a hazard to human activity. In the Middle Ages, however, they were often used as natural terrain obstructions, for example defending strongholds. In the southern part of the Racibórz-Oświęcim Basin, landslides formed steep hillsides on which seven defensive structures were located. Landslides were even activated in the immediate vicinity of their ramparts. Landslides were even activated in the immediate vicinity of their defensive walls. The natural defensive values associated with landslides should be considered: their steep, sometimes vertical main main scarps, uneven surface of the landslides, bogs found in niches, watercourses and reservoirs, as well as complexes of forest vegetation with numerous thickets with fallen trees. In the neighboring valleys, murshy or flooded bottoms of these forms were an additional obstruction. In addition to physical features, archaeologists also point to the psychological aspect of such places, causing uncertainty and fear among the invaders. The article presents the share of individual types of field obstructions in relation to the studied objects. The studied defensive structures functioned for three periods: (1) during the tribal state of Goleszyce, (2) during the transitional period from the invasion of Great Moravia to Goleszyce to the strengthening of the state of the first Piasts, and (3) in the late Middle Ages, when the role and importance of ancient strongholds changed. In some cases, such as in Lubomia or Raszczyce, reactivation of landslides caused problems in maintaining of slopes behind the defensive wall and ramparts in good condition. In the case of Czyżowice, the knight's stronghold was completely destroyed by landslide processes. Castles usually fell due to invasions after which they were abandoned. In Piel-grzymowice, the earlier defensive structures were transformed into a cult center. Similar to the study area, terrain conditions related to landslides were used for the location of strongholds belonging to tribal countries in Pomerania, Warmia and Mazury, and even by the Teutonic Knights in the Dobrzyń Land.