A sudden desire now seized Alexander to visit and consult Ammon in Libya, both because the oracle of Ammon was said to be truthful and because Perseus and Herakles had consulted it… . Alexander was engaged in a rivalry with Perseus and Herakles, as both heroes were his kinsmen. Moreover, he sought to trace his own birth to Ammon, just as the myths trace the births of Perseus and Herakles to Neus. In any case, he set out with this in mind and imagined that he would obtain more precise knowledge of his own affairs, or at least would say he had obtained it.
(3.3.1-2), The Landmark Arrian: The Campaigns of Alexander, translation by Pamela Mensch, and used for all quotes and references to notes.
Alexander’s “sudden desire” has seized him several times already in Arrian’s history, most recently in the form of a “sudden passion” to found the city of Alexandria in Egypt. Look for variations on this phrase (it has appeared several times already)—from a literary standpoint it provides a basis for Alexander’s increasing impetuosity. Continuing the imputation of Alexander’s desires, Arrian notes the shift in Alexander’s mythical/divine comparison—he seems no longer content in being associated with Achilles and actively seeks to be associated with Herakles. (Later in Arrian’s account Alexander makes the association more with Dionysus—a progression from a son of a god to the son of Zeus to a god.) The comparison with Herakles has previously appeared in his dream before the siege of Tyre, but it’s the last clause in the quote, “at least would say he had obtained it”, that stands out for its ambiguity. While open to interpretation, I don’t believe Arrian meant that Alexander would lie about the oracle since Arrian makes it clear in the work’s opening that it was more disgraceful for a king to lie than anyone else. Another interpretation of this phrase isn’t so cynical and has to do with the ambiguity of oracles. My guess is that Arrian references a doubt that anyone, including Alexander, can claim to interpret oracles precisely. This option makes more sense for Arrian’s comment here and the related one at the end of the next chapter.
In addition to why Alexander chose this detour to the oracle, an obvious question is “why now?” One of Alexander’s most effective traits as a general has been his speed in moving the army and his tenacity once engaged. These traits appear often, especially during his pursuits of Darius and Bessos later in this book. He has had success at the Granicus River and at Issus, successfully besieged Tyre and Gaza, and secured Egypt. Why not press the battle directly to Darius at this point instead of providing additional time for Darius? Obviously there is no way of knowing what Alexander was thinking but the delay caused by the sieges cost him about a year, already providing time for Darius to regroup and possibly diminishing any sense of urgency for a confrontation. Add Alexander’s mastery of self-promotion and pragmatism when an opportunity arose and he must have seen the trip to the shrine of Ammon as a way to elevate his standing to friends and foes alike while calculating (correctly) that Darius wasn’t going anywhere.
The trip to the oracle provides several opportunities for the gods to assist Alexander, at least according to the sources Arrian uses. A statement such as “And I can confidently declare that divinity aided him in some way, since such a view accords with what one might reasonably expect” says more about Arrian’s opinion toward Alexander than the veracity of the sources. It’s as if the oracle’s reply is of secondary importance, somewhat confirmed when he says that Alexander “heard what his heart desired (as he said)”. In addition to my interpretation noted above, this phrase provides (probably) unintended irony since Arrian has provided two examples of the listener hearing what they wanted to believe, first by the Thebans upon hearing Alexander was dead (1.7.3) and then by Darius following advice to leave the favorable ground at Sochoi (2.6.6). Nothing good came from the Thebans or Darius hearing what their heart desired.
Cross-posted, with minor changes, at Reading Odyssey