"And what was he doing crossing that forsaken desert?" They weren't 'crossing,' they lived there. There are hundreds, perhaps thousands of these mummies out there. This region, in which the mummies were found, is twice the size of Texas.
Certainly had an odd choice in real estate, though I suppose things were probably far different back then...here's a random thought: what if most deserts are like the ones in the Fertile Crescent, resulting from prolonged agriculture?