Jason and the Argonauts (1963)

Directed by: Don Chaffey

Cast: Todd Armstrong, Nancy Kovack and Gary Raymond

 IMDb page about Jason and the Argonauts

Studio(s): Shepperton Studios - S.A.F.A. Studios, Rome

Trailer:

The true star of the movie is (as is often the case with his projects) is Ray Harryhausen, the legendary animator who created scenes such as the skeleton fight sequence virtually single-handed. This sequence alone involved 4.5 months of animation with skeleton figures barely 8 inches tall. Harryhausen was also heavily involved in the live action shoot, which took place on location in Spain. 
The scene was rehearsed with the actors fighting live stand-ins for the skeletons. When the cameras rolled, the stand-ins stepped aside, leaving the actors to repeat their moves fighting thin air.
Ray Harryhausen worked with that live action material projected onto screens behind his skeletons.