Orientale imperium A Note on the Dating of the Historia Augusta

The life of Aurelian in the Historia Augusta includes the expression Orientale imperium, which is very rare in classical and late antique Latin texts, with as few as nine/ten occurrences, mostly in the sixth century and none earlier than the 410s. It appears in a passage which is clearly taken from Festus' Breviarium or Jerome's Chronicle, both of them using Orientis imperium. The change made by the author of the life of Aurelian can be justified only if he adopted a term which was sufficiently widespread in the political communication of his times to be considered as a perfectly understandable synonym of “Eastern Empire”. This might indicate a later dating for the Historia Augusta, or at least for the passage where Orientale imperium appears.