Several fortresses were erected in Aargau between the 11th and 14th centuries which served their builders as well-fortified residences and centers of possessions organized in terms of power. Most of these facilities were erected without participation by the Hapsburgs. However, in the course of the 14th and 15th centuries, many fortresses were enfeoffed to Hapsburgs.Little remains of the earliest fortresses. Wooden structures, like the one which has been verified in Hallwil, can only be ascertained archaeologically. Stone structures of the 11th and 12th centuries were in many cases replaced by newer buildings at a later date. The numerous megalithic towers, like those in Aargau (i.e., Aarau/Schlössli, Habsburg, Hallwil, Auenstein) date from the 13th century.