Salve,
I would just like to recommend a book I was reading the other day on seemingly misunderstood Emperor. "Gallienus" by John Bray, sheds a new light on an Emperor whose life, up until now, was derived almost entirely from the Historia Augusta. I found the book to be a revealing insight not only into the man, but also into the bias against him in the works of historians. I would strongly recommend it to anyone interested in the period of Aurelian and the Soldier Emperors, but also as a purely interesting historical read. A bonus is that it is also usually fairly cheap to purchase (Although mine was an exceptional case, in that I managed to get a copy for AUS$10 in mint condition (brand new)).
Hope this helps someone.
Vale bene,
Marcus Ulpius Trajanus