Changes

* Birley, Anthony R. <i>Septimius Severus: The African Emperor</i> (London: Routledge, 1999)* Campbell, Brian. <i>The Roman Army, 31 BC-AD 337: A Sourcebook</i> (London, Longman, 1997)* Grant, Michael. <i>The Severans: The Changed Roman Empire</i> (Routledge, London, 1996)* Hekster, Oliver, <i>Rome and its Empire, AD 193–284</i> (Edinburgh, Archer Press, 2008)