While the above is litho is indeed beautiful, I was remembering that I had seen another version (same imagery) but with a bit more detail (note the rider on the horse and the horse itself, and the figure on the right, as a couple examples).
I'm thinking this version was the first release OS, that was created. The one above, was a later RR, redone/redrawn, but based on this poster art.
This, to me, is another stunning and amazing poster. It gets two of these..