The Desert of the Tartars (1976) on Netflix

Lieutenant Giovanni Drogo is assigned to the old Bastiani border fortress where he expects an imminent attack by nomadic fearsome Tartars.

As his first assignment, lieutenant Drogo is sent to an isolated fortress on the borders of a desert and of a range of high mountains. The mission of the garrison is to prevent a possible incursion by the fearsome Tartars, coming from beyond the desert. Some fellow officers are eagerly awaiting an attack; some no longer want to believe in it; others take advantage of the vague threat to further their career. All of them are sacrificing everything -- health, youth, friends, family -- for a distant military ideal: leading the defence against the onslaught of the enemy. But in the vast emptiness surrounding the fortress, nobody has ever sighted the Tartars...

—Eduardo Casais <casaise@acm.org>