For in all battles the eyes are vanquished first
"by means of terror and shadow of a ghostly army they cause panic, since no enemy can bear a sight so unexpected and hellish"
Tacitus, on the Germanic "ghost warriors" the harii. (Who, by the way, are what Simek calls "the obviously living armies of the dead," the historical, black-clad, flesh and blood foundation for the mythic conception of the Einherjar.)
Alternate histories of special effects, lightless guerilla warfare, the trompe l'oeil such that the night itself will rout the empire. A haunted house theater of operations / of cruelty.