Alexander's oracle temple of Amoun is the most important remaining temple at Siwa. At first we should talk about Alexander the great and his plan on how to invade such a glorious and solid nation like ancient Egypt. In 331 B.C when Alexander Came to Egypt, he did not spend much effort about how to defeat the Persians who took over the power few years earlier, he focused on the Egyptian people and knew they are the key to the great empire not the Persians!!
That was the reason why he has chosen Siwa to be the first destination within Egypt as it is isolated and not very busy. Alexander thought Siwian did not see the real Egyptian king in reality, and if there was a link between Siwa and the Nile's valley enabled them or the king to see each other, it would be the same link enabled them to know about the Persian invaders, and the killing of the king, and in both options Alexander can get in Siwa safely! From this point Alexander the great needed this plan of "the oracle".
The oracle was for confirming Alexander the great to be the son of Amoun like the ancient Egyptian king tricking the Siwian people or giving them hope.
Guarded by the Greek army, Alexander went to the temple of Amoun and got inside the chapel alone to receive his oracle. The son of Zeus was then in his path to be son of Amoun as well!
Nobody knows what the oracle told Alexander; politically the answer was whispered into his right ear. But it probably was confirmative; Alexander expressed ever since a wish to be buried at Siwa "was also diplomatic", and he embarked upon great conquests in the east, conquests that only a son of a god would dare to embark upon.
The Oracle temple of Amoun is very small in size regardless of the surrounding campus. It was one of the 6 most influential in the known world of those days. It probably came into use some time in the 6th century, as an expansion of the up to 200 years older temple dedicated to Amoun-Re.
The impact of this site in ancient times appears slightly strange and fascinating at the same time to modern visitors. The actual temple is so small, but the entire setting is like out of a fantasy novel. The temple complex, complete with a well (quite well-preserved) takes all of a little mountian rising up from the oasis. Seen from a distance, the site is like a white island floating on green palms. Upon entering, a wall rises above you, and when standing next to the temple you will have fabulous views.
Unfortunately, there is little to fascinate a visitor with the temple structure itself, no wall-paintings and no fine details have survived. It is best when seen from a distance.
The temple itself is really very small, but as most visitors never were allowed to enter, just stand on the ground 12 meters beneath, it probably appeared to be quite impressive.