The Desert of the Tartars (1976) on Netflix

Plot summary

Giovanni Drogo is a young lieutenant whose first posting takes him to the Bastiani fortress, a medieval castle on the frontier of an empire, with the desert of the Tartars stretching away in front of it. The garrison exists to prevent an incursion by the Tartars, a feared people nobody has ever seen there. Drogo's fellow officers divide over the vague threat: some wait for the attack, some have stopped believing in it, and others use it to advance their careers. The outpost runs on ceremony and routine, and the men posted there bicker continually; isolation wears at them over the long wait.