Any good historical novels set on the 3rd Century Crisis?

I'm not sure if this is the right forum to create this thread, but, anyways, i'm looking for some historical novels set during the Crisis of the Third Century, on the Roman Empire. I'm appalled by the apparent scarcity of novels about such a fascinating period, while there are a hundred books set in Roman Britain or in the Late Roman Republic. I've read many books dealing with the final decades of the Republic (Colleen McCollough, nuff said), and have found some good ones set in Late Antiquity (Gore Vidal's Julian is brilliant, and William Napier's Atilla series).

So, does anyone knows works set in this gap? Anything from Alexander Severus' reign to the ascension of Diocletian is fine (perhaps something on the reign of Gallienus, Claudius II or Aurelian).

A couple ones i found were: Nick Brown's "Siege" (first of the Agent of Rome series) and Valerio Manfredi's "Empire of Dragons", but neither of them seems to focus on the Roman Empire itself (can't say for sure, as i haven't read them).

Nope not a lot of good novels in that period.

If your interested in anything around Claudius time check out the Eagle series by Simon Scarrow. More than 10 novels now I think. Great series.