One of the many fun things about this movie is the giant flying head that gathers
tribute amongst the savage humans who dwell outside of the Vortices. The head is a god called Zardoz
Some of the savages, such as Sean Connery, are the priests of the giant flying heads and wear papier maché helmets identical to the head while they ride about on horseback and pillage the other savages.
Connery leaps into the maw of the head and is whisked off to the village of the Eternals. While they decide what to do with him, he roots about and discovers that the entire social structure which condemns some humans to live in benighted ignorance while others loll about in silken togas is based on an old story: L. Frank Baum's novel The Wizard of Oz. Zardoz is just an empty figure head. Well, flying head.
One of the greatest things about this movie can only be found in the Japanese dubbed version from so many years ago: The actor playing the Sean Connery character actually tried to imitate his voice, slurred sibilants and all. "Zhardosh."