The valley of the dead Gat, located in the south of Gironde, is dotted with numerous medieval fortifications called "motte castrale". It is a earthen ground, generally artificial and surmounted by a wooden keep. Sometimes considered to be a "primitive fortified castle", the mound appeared in the year 1000 and was gradually abandoned in favor of stone castles.
The Casterasses mounds, built in the town of Cabanac, are an original example and are particularly well preserved. The site is established on the left bank of the dead Gat and therefore had to control this navigable axis, as well as the dirt road which borders the site to the north.
The Casterasses are a defensive unit made up of a frustoconical mound 10 meters high included in a low quadrangular courtyard and flanked by a second mound. This one leans against the western flank of the farmyard without cutting it. This configuration is unique in the region, where most of the earthen defense sites are simple clods or associated with a farmyard.
The two clods are surrounded by ditches which are now partly filled. According to legend, fairies come to wash their clothes at nightfall in the spring that springs from the western ditch ...
Archaeological research has been undertaken to enhance the site and restore it to the public.+