It draws on accounts in Suetonius's "Life of Vespasian", Tacitus' "Histories" (III, 78) and other ancient Latin historical texts on the Jewish Revolt, stating that Vespasian went to an unnamed priest living on Mount Carmel for a prophecy about the outcome of his campaign. However, the painting's main source is the re-reading of the episode in Carmelite literature, which gives the priest the name Basilides and sees him and Elijah as antecedents of their order.