Around 524 BC, a Persian army of 50,000 strong disappeared in the Egyptian desert in what is one of the greatest archaeological mysteries of all time. Now, an Egyptologist has finally solved this vanishing act.

Leiden Professor Olaf Kaper made this accidental discovery while conducting his decade-long excavation in Amheida, in the Dachla Oasis of Egypt. He unearthed ancient temple blocks detailing a full list of titles of Petubastis III, an Egyptian rebel leader, and let the puzzle pieces "fall into place." It turns out that the army's disappearance was really just a cover-up.

According to the writings of anchient Greek historian Herodotus, King Cambyses led his Persian troops into the desert near Thebes (modern-day Luxor) and never returned. Supposedly, they were swallowed by sand dunes, but this myth has long been debated.

Egyptologist Kaper, for one, never believed it.

"Since the 19th century, people have been looking for this army: amateurs, but also professional archaeologists. Some expect to find somewhere under the ground an entire army, fully equipped. However, experience has long shown that you cannot die from a sand storm, let alone have an entire army disappear," he said in a Universiteit Leiden news release.

Based on his discovery, Kaper now argues that the army didn't disappear but was defeated. His research indicates that the Persians were not simply passing through the desert, but were headed for the Dachla Oasis. There, Petubastis III and his troops were waiting.

"He ultimately ambushed the army of Cambyses, and in this way managed from his base in the oasis to reconquer a large part of Egypt, after which he let himself be crowned Pharaoh in the capital, Memphis," Kaper explained.

Persian King Darius I later ended the Egyptian revolt two years after Cambyses' defeat. Rather than upsetting the newly restored balance, he attributed the shameful defeat of his predecessor to natural elements. It is because of this manipulation of historical events that the army's fate has remained a mystery for 75 years.

"The temple blocks indicate that this," Kaper said, referring to the Dachla Oasis, "must have been a stronghold at the start of the Persian period. Once we combined this with the limited information we had about Petubastis III, the excavation site and the story of Herodotus, we were able to reconstruct what happened."

The discovery will be announced on Thursday at an international conference.