But the Siwa reference is absolutely connected to Alexander's exploits. The oasis at Siwa was home to the world renowned Oracle of the god Amun (Ammon) described in Herodotus' Histories.
At the beginning of his campaigns Alexander took a side trip there and legend (Herodotus) says was saved by a rare thunderstorm.
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.
According to legend, wasn't Alexander's body supposed to have been buried in Siwa after his death in Persia?
I think some Italian archeologists are looking for his tomb somewhere out there in the desert.