On a fall night before Issus in 333 BC, we are told by Curtius Rufus, Alexander ascended by torchlight to the summit of a lofty mountain, and in accordance with ancestral custom performed sacrifices to the chief guardian deities of the place: an intriguing historical remnant, the more challenging because Curtius provides no other details, and no other Alexander account gives reliable information about this particular display of piety. Consequently the gods in question remain unknown. The purpose of this study is to establish the likelihood that Alexander did in fact perform these rites, and to determine the probable identities of the deities in the light of what is known about religious cults at Issus before he arrived.