Harii

The Harii (Latinized West Germanic "warriors") were, according to 1st century CE Roman historian Tacitus, a Germanic people. In his work Germania, Tacitus describes them as painting themselves and their shields black, and attacking at night as a ghostly army, much to the terror of their opponents. Theories have been proposed connecting the Harii to the einherjar, ghostly warriors in service to the god Odin, attested much later among the North Germanic peoples by way of Norse mythology, and to the tradition of the Wild Hunt, a procession of the dead through the winter night sky sometimes led by Odin.

Germania

Regarding the Harii, Tacitus writes in Germania:

As for the Harii, quite apart from their strength, which exceeds that of the other tribes I have just listed, they pander to their innate savagery by skill and timing: with black shields and painted bodies, they choose dark nights to fight, and by means of terror and shadow of a ghostly army they cause panic, since no enemy can bear a sight so unexpected and hellish; in every battle the eyes are the first to be conquered.