Cassius Dio, Roman senator of Greek descent, historian, lived from 155 (163?) to c.325 CE, and thus was eye witness to the reigns of Marcus Aurelius to Elagabulus.
This era is covered in Epitomes 72 through 80 in his Roman History.
This apropos our upcoming discussions about How Rome Fell: Death of a Superpower by Adrian Goldsworthy.
Image: Bust of Marcus Aurelius (reign 161–180 CE), Glyptothek Munich