Celebrations of the two main festivals of the Iranian calendar, Nawrūz and Mihraǧān, are part of the general phenomenon of presence of Iranian strands in social and political culture of the Abbasid centuries. Through a critical approach to the sources, the author verifies the assumption that Iranian festivals were a politically relevant element of Abbasid culture and customs. The political relevance of Nawrūz and Mihraǧān is then discussed with regard to its relations with contemporary Islamic political discourse as a whole, in order to verify two recent interpretations of Islamic political theory and practice in the formative centuries. Sources hereby considered lead to the conclusion that Nawrūz and Mihraǧān are clearly embedded into Abbasid political discourse. Those festivals, in fact, concurred to the construction of a hierarchic legitimacy. At the same time, incompatibility or competition between them and Islamic political theory remained merely exceptional.