______One enduring mystery of pre-Roman times was the disappearance of an entire Persian army. The Lost Army of Cambyses marched towards the Egyptian oasis at Siwa around 520 B.C. and hasn't made it there yet.
______Cambyses II, Emperor of Persia, conquered Egypt in 525 B.C. and installed his family as the ruling 27th Dynasty, having rid himself of Psamtek (bless you!) III, the last truly Egyptian ruler of Egypt until the 20th Century. There are some disputes as to why Cambyses decided to invade Egypt, but all of them revolved around women.
______In any case, Cambyses DID invade and defeated the Egyptians. He then spent the next three years of his short rule doing just about everything he could think of to inspire hate in the Egyptian people. After several military disasters, including an ill-fated invasion of Ethiopia, he wasn't terribly popular with his own Persians either. A revolt back in Persia would eventually lead (indirectly) to his death.
______But before that Cambyses sent an entire Army out into the Sahara Desert to Oasis Siwa. One mystery is WHY? Was it so he could use it as a base for invading Carthage next? Was it to destroy any lingering Egyptian resistance? Or was it to legitimize his rule by seizing the Oracle of Amun, which was located there?
______Supposedly 50,000 men left for the oasis. In addition to Persians there were undoubtably mercenary units from Greece, Phoenicia, Syrians, Cilicians and dozens of others ethnic groups then under the heel of Persia.
______The soldiers of Cambyses were well-armed with swords, spears, chariots and other weapons which represented the cutting edge (pardon?) of the military technology of the time. So it is extremely unlikely that an enemy force intercepted and destroyed them. It is possible that the soldiers got lost or were trapped in a sandstorm, but SOMEONE should have either reached Siwa or returned to the Nile. Instead, the entire force disappeared without a trace.
______Several expeditions have been sent to find the lost army, no doubt beginning with Cambyses himself. But treasure-seekers, tourists and archeologists have searched the Sahara trying to find the remains of these forlorn soldiers for over 2,500 years now with no luck. Archeologists are particularly keen to find the remains as it is anticipated that the soldiers' personnel effects would be particularly well-preserved in that climate. Assuming the soldiers weren't kidnapped by UFOs or marched south to establish an empire in Zimbabwe!