Video from 2009.
"It is one of the greatest archaeological mysteries of all times: the disappearance of a Persian army of 50,000 men in the Egyptian desert around 524 BC. Leiden University Professor Olaf Kaper unearthed a cover-up affair and solved the riddle." Source: Science Daily (2014).
Note: See "Cambyses II, the Persian Ruler of Egypt (27th Dynasty) And His Lost Army" for the relevant background.