"...'Did intelligent beings from outer space visit Earth thousands of years ago?'
"If not then who, or what built massive stone structures, tens of thousands of years old, scattered throughout the world?"
The series is based on and inspired by the works of Erich von Däniken and Zecharia Sitchin, among other writers. The works of Graham Hancock, Robert Bauval, Brinsley Le Poer Trench, Charles Hapgood, and Edgar Cayce, are also referenced in many episodes.