DESCRIPTION:
This is a song from movie Conan the Barbarian (1982), based on the stories of Robert E. Howard and directed by John Milius.
Roles (not all of them, but the main ones):
Arnold Schwarzenegger - Conan
James Earl Jones - Thulsa Doom
Gerry Lopez- Subotai
Sandahl Bergman - Valeria
Mako Iwamatsu - Akira

This song cannot be found as a soundtrack and I've spent quite a lot of time looking for it.
In a part of the movie where Conan, Subotai and Valeria are stealing the Eye of the Serpent there is medieval music playing and the cultists are singing.