The Augustan History and The Onion

The problem with history as a source for fiction is that a lot of history is already fiction.  Or, rather, we have no idea how much of it is fiction.

Consider what we know about the Roman Emperors of the Third Century, that melancholy time of civil wars and usurpations.  Written sources are extremely rare and fragmented.  A lot of what we think we know comes from the Historia Augusta, a motley collection of tales that mixes what seem to be real documents with a lot of stuff someone might well have made up.  No one is even sure when it was written--it bills itself as a collection of six historians made during the early Fourth Century, but no one seems to believe this anymore.  The putative author of this weird work (which I've never read--but all authors on the period have to cite it) might make a good character in a historical novel.  What was he after?  Is the Augustan History something like The Onion?  Incidentally, The Onion would be a superb source on the spirit of our era, if you could pass its distortions and heightenings through some kind of reverse filter.

So would The Simpsons, for that matter.  These channels are sensitive to the zeitgeist in a way more deliberate journalism isn't.

Is the author of the Augustan History still mocking us after all these centuries.  Is one of those Emperors completely made up?  If so, which one?