For the narrative of Alexander and Darius at Issus see Arrian, Anabasis Alexandri, trans. E. Iliff Robson. Loeb Classical Library. (London: Heinemann/ New York, Putnam & Sons, 1929), II:iii-xii; Quintus Curtius Rufus, History of Alexander I: Books I - V, trans. J.C. Rolfe. Loeb Classical Library. (Cambridge: Harvard University Press/ London: William Heinemann, 1962), Book III. Brueghel follows Quintus Curtius's account: Arrian describes Darius as fleeing in his golden chariot, as we see in Altdorfer's famous picture of this subject, but Quintus Curtius says that he left his chariot when the horses panicked, and instead fled on horseback and this is exactly what Brueghel shows.