It was a historical drama directed by Leon Klimovsky, written by Paul Naschy and co-produced by Nestor Gaffet and Jose Antonio Perez Giner.
Naschy said he based the lead character Gilles de Lancre on the notorious medieval serial killer Gilles de Rais, and the film's plot was a loose remake of the 1956 Akira Kurasawa film Throne of Blood (itself an adaptation of Shakespeare's Macbeth).
It was filmed in May and June 1974, and was theatrically released only in Spain and Belgium that same year as El mariscal del infierno.
[1] In medieval France, the Baron Gilles de Lancre becomes obsessed with alchemy and black magic, and his wife (the sadistic Georgelle) encourages his interests, fooling him into believing that an alchemist friend of hers named Simon de Braqueville can change lead into gold if the Baron will supply him with a quantity of virgins' blood to use as an ingredient.
The Baron orders his soldiers to kidnap any young virgins in the area, and his wife has the girls violently sacrificed in ways that satisfy her own sadistic urges.