Augustan History
The phrase "de Jure Fisci et Populi" appears anomalous, but it occurs elsewhere. (See Paulus, "Recept. Sent." 5.12.) The "Augustan History" also ("Alex. Sev." 15) says that Alexander Severus "leges de jure populi et fisci moderatas et infinitas (?) sanxit." Probably under the phrase "jus populi" must here be understood the law relating to the "aerarium", or to the "arca publica" (which latter, practically as well as theoretically, was at the disposal of the senate) as distinguished from the "fiscus", which was the emperor's own, not as "res privata", but as property attached to the imperial dignity. ("Augustan History", "Aurelian" 20.)