Two fundamental features of the Sasanian monumental art, i.e. the realism and positional tradition, have been represented in rock reliefs of that time in the best manner, so that they have created a semiotic cryptic system together. Concept mining of this semiotic system will be achieved by appealing to a context-oriented approach and benefiting from the contextual continuum (comparative picturology). What underlay this research was the optical illusion resulted from implementing the perspective in the rock relief of Bahram II in Naqsh-i Rustam, Fars. This issue, which has misled the researchers in characterology of some figures, is highly controversial. Why the Sasanian artist has sometimes intentionally implemented an unnecessary perspective? Results of the studies indicate that artistic tricks such as perspective have also played the role of a sign in these artworks; as this trick in Bahram II rock relief in Nadsh-i Rustam, without any perspective, is merely accompanied by a political implication based upon the right of crown prince. The objectified perspective in the rock relief of Shapur I in Naqsh-i Rajab, Fars province, is also the evidence indicating the priority in the right of crown prince position.