The research reconstructs the contribution of the imperial normative activity to the definition and evolution of the "crimen falsi" between the first century A.D. and the Severian age. The first part of the volume is dedicated to the reconnaissance and cataloguing of all the evidence preserved in the legal sources expressly attesting to imperial interventions about "falsum". In the second part, an exegesis of the "constitutiones principum" identified is carried out, with particular attention to the relatively numerous interventions on the subject "sibi adscribere in testamento alieno", falsification and the use of fake and "instrumenta falsa" in commercial relations; a final section of the work is dedicated to the other cases of falsum of which the sources provide information on imperial interventions.