Jason and his men have begun to backtrack.
Here we see them in frame with the Skeleton warriors.
The columns could be either set or bi-packed. I'd guess set based on shadows which match the skeletons.
This above shot is possibly the most critical in selling the effect.
Aeetes cheers them on.
Also note the classic editing/storyboarding: mixing wide with close shots.
Drawing out the tension before the fight.
Here's where I should also tip the score. Bernard Hermann (best known for his Hitchcock scores).
The skeletons are not being treated as an effects shot, but just as any fight opponent.
Aeetes, again. Great blue sky.
In a few days we'll show the fight ensuing.