Two years after the incident at Gordium, Alexander would head south into the Saharan desert in today's Egypt and Libya in search of the oracle of Zeus-Ammon at Siwah. Greeks and Egyptians both venerated the temple of Zeus-Ammon, and Siwah, an oasis surrounded by the Libyan Desert, was believed to be the abode of the Egyptian gods....
....it was an arduous, two-hundred-mile journey from the vast tract of sand where Alexander would soon found Alexandria-in-Egypt through the inhospitable desert. By day four of their eight-day journey they had run out of water, only to be saved by a sudden rainstorm. They lost their way, only to be saved by the flight of two crows that had been spotted. When they reached Siwah...Alexander...was taken directly to visit with the oracle. The high priest...is alleged to have greeted him as the "son of Zeus-Ammon." Historians have again debated whether the priest said "my son," or "son of Zeus-Ammon," or "son of God," or if it was just a slip in translation. We shall never know. Suffice it to say, Alexander used it to full effect, and from that day on Macedonian spinmeisters stressed his divine roots.
May I recommend to you "In the Footsteps of Alex. the Great" - an excellent visual journey in DVD format now. It traces his campaigns throughout Africa and Asia...includes the Siwah journey.