The underground passages are our principal study.
Underground, it means that man had dug it in the ground, and the underground passages are built with facilities in the walls. These facilities were made in order to use them during the occupation of the cavity. The underground passages are often galleries and little rooms making a network more or less large. They are totally made in the rock. Their real function remains relatively difficult to explain regarding their remains discovered today.

Nevertheless we can identify 2 groups : the underground refuges (souterrains-refuges) and ring-shaped underground (souterrains annulaires).

The underground refuges constituted local underground fortresses, dug during murky chapter in history, made in our country to shelter a community (inhabitants of farm, of hamlet, of little castle) and also with all means of subsistence (live stock, grain). It was difficult to take the underground refuge without heavy losses in men. It was a good way to protect them from pillagers. Thanks to defense systems we can classify them in 2 groups : underground refuge with passive defense (the most ancient of them date from 13th century) and underground refuges with active defense (they date from 14th-16th century).

The defense systems in the underground refuges with passive defense is composed by several obstacles (doors, narrow passages) or by traps (wells, silos). The defense system in the underground refuges with active defense is more complex using loopholes. For example, because of fire through the loopholes, the assailant was not able to destroy the doors and enter the rooms.

The characteristic of the ring-shaped underground is that the gallery has the shape of one or several rings. It seems that they have no storage or refuge function. At the moment, we are thinking that they were probably used like places for worship of dead men, of fertility in connexion with the Earth mother (Terre Mère) between 10th and 16th centuries.