C. or Casa dei Cröisch is the name given to a number of small defensive structures in the Blenio Valley, which are built in caves or under balms. Both names and variants also stand for undeveloped caves as well as for old buildings and ruins within and occasionally outside the Blenio Valley. The fortifications known today are located in the former municipalities of Aquila, Dongio (three), Malvaglia, Marolta and Torre. The building called Castello in the former municipality of Chiggiogna in Leventina, which neighbors the Blenio Valley, belongs to this group due to its location and structural features. All systems except one are in a clear spatial area. Relationship to a settlement. They are difficult to access and are usually additionally protected by truss-like walls. The vestibule, fireplace and small finds prove that it is habitable. In addition to the preserved, irregular mortar masonry, several of the buildings were partly made of wood. Numerous controversial hypotheses about the population and function of the C., such as signal posts, refuges of the last pagans or Saracen bases, were based on its location or its name. In folklore. In this respect, the buildings, with the legendary tradition of the pagans living on the C. living in the valley, similar to the Grottes aux Fées in Valais, are closely related to the idea of motherly. powers. Since the written sources are silent, the interpretation remains archaeological. Finds and findings: According to two C-14 dates that have not been further confirmed, the building can be dated to the 3rd-7th century. (Malvaglia), or 9th-11th. Century (Dongio 1). After thorough Although the C. of Malvaglia was destroyed around 1200, it was rebuilt and probably served as a residence for members of the local ruling class until the 14th or 15th century.