Engraved on the tympanum of Romanesque churches, on the lid of early Christian sarcophaguses, drawn at the beginning of charters and diplomas or inscribed on seals, the chrismon is an omnipresent motive in medieval artistic and cultural manifestations of the western Middle Ages. It occupies a particular place in monumental sculpture in the South of France and in the North of Spain where it contibutes to the decoration and general organization of buildings. Until today, Art history has not really submitted the motive to a formal analysis and to an interpretation of its meaning. Most of the studies about the chrismon have been made in the framework of Medieval epigraphy, as a particular form of medieval writing. Generally, the chrismon has been studeid in an evolutionist perspective and tried to point formal and semantic transformations of the motive, from the simple Constantin's labarum to the complex sign of Romanesque portals. This limitation to the search of a meaning and its evolution has taken the studies apart from analyzing the nature of this sign. There is, until today, no genetic analysis of the chrismon as significant, but many attemps of explanation, more or less applicable to medieval symbolic reality and to its graphic forms. By analyzing the inscriptions engraved near the Romanesque chrismons and looking for common factors allowing to gather very different forms and fonctions of this motive, this paper would like to propose some runways for the understanding of the semantic value of the Pyrenean chrismon and for its role in monumental implementation of sculptured decoration.