The 3rd century historian Herodian of Antioch wrote a history in eight books of the emperors from the death of Marcus Aurelius to the accession of Gordian III. The 1961 English translation is now online here. This is out of copyright in the USA, so copy freely if you are based there.
Roger Pearse
Thoughts on Antiquity, Patristics, putting things online, information access, and more