The Unknown Zone: Garamantes the Lost Civilization of modern day Libya.

Long before Southern Libya was part of the Sahara Desert, it was a lush Savanna for thousands of years.  Then climate change (pre manmade!) took hold and the area fluctuated between arid and wet from 8000 to 3000 years ago.  The inhabitants learned how to tap into the underground water system and created a vast network of underground canals to irrigate their fields and created an empire of 3 large cities and many smaller "towns" in an area the size of North Dakota.
Who were these people and what happened to them?  Judy Sellins and Dave Turco will then link this lost civilization to the many lost cities of North America in the never ending battle to bring to light past advanced societies that academia says couldn't have existed.