The word ‘boundary’ does not only indicate a physical division between different worlds. The border often represents a point of contact. This concept of a ‘boundary’ is particularly critical in the field of legal history because often the plurality of iura contributes not only to the fusion of different cultures but also to the creation of new ones. The purpose of this paper is to investigate the relevance and the meaning of expressions of Anathema and curse it’s possible to find in some Latin documents that date back to the Norman period of Sicily. This period is pivotal for the consolidation of the secular and spiritual power of the Church and the use of curses by the lay power highlights a blurred line between the ecclesiastical and the temporal power. This idea of power makes the very strong ecclesiastical character of early political thought understandable. Going through some documents, this paper aims at understanding, from a legal point of view, the meaning of these curses: are they simple notary formulas, without legal significance or, as penalty clauses, a fundamental part of legal documents?