Gibbon, Edward, The Decline And Fall Of The Roman Empire, Vol. 1. Chapter 6.
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Glen Warren Bowersock, Roman Arabia, Cambridge, Harvard University Press, 1983, pp. 126–128, ISBN 0674777565[1]. "with the last of his names, he clearly tried to forge a link with the ultimate Antonines, who were the Arab emperors from the family of Julia Domna"
Maxime Rodinson, The Arabs, Chicago, University of Chicago Press, pp. 55, ISBN 0226723569, [2], "The emperor Septimus Severus married an Arab from Emessa, Julia Domna, whose sons and great-nephews ruled Rome."
Herodian's Roman History, chapter 4.11: Caracalla's Parthian War, translated by Edward C. Echols (Herodian of Antioch's History of the Roman Empire, 1961 Berkeley and Los Angeles), online at Livius.org
