A security paper comprising a fibrous substrate comprising a watermark having repeating motifs, and a security structure that does not completely cover the watermark and has at least one semi-reflective area which is superposed at least partly on the watermark; which paper on the one hand allows observation, through the semi-reflective area, at least partially, of one of the motifs, and on the other hand allows observation at least partially of another of said motifs in a region of the watermark that is not covered by the security structure.