A god goes into battle wearing a helmet, and the helmet's gift is not protection but disappearance: the wearer moves through the fight unseen, striking from nowhere. The object that hides its bearer is one of the oldest advantages myth can grant, and here it belongs to the war of the gods against the giants.

The witness is Apollodorus's Library (a Greek mythography compiled in the 1st–second century CE). Earth, enraged over the Titans, brings forth the giants, matchless “in the bulk of their bodies and invincible in their might”, serpent-footed and hurling burning oaks at the sky; an oracle warns that no giant can fall to a god's hand alone, but only “with the help of a mortal”. So Zeus summons Hercules, and the gods divide the giants among themselves. In the roll of killings—Apollo taking one eye of Ephialtes and Hercules the other, Dionysus felling Eurytus with a thyrsus (a wand tipped with a pine cone), Poseidon breaking off a piece of an island to crush Polybotes—one line names the vanishing helmet: “And Hermes, wearing the helmet” “of Hades,” “slew Hippolytus in the fight”. The cap belongs to the lord of the dead, and its virtue is spelled out in the accompanying note: “The helmet of Hades was thought to render the wearer” invisible, the editor adds, pointing back to Homer's Iliad and the Shield of Hercules where the same dark headgear appears.

That the helmet's power reaches us through the editor's gloss rather than the bare narrative is the one thin place here: the story-text simply says Hermes wore it and killed, trusting the reader to know what wearing it meant. The address's other authority, an Icelandic one, waits unread on the shelf.

An invisible killer needs no shield and fears no blow; he can strike and never be struck back. Why does myth so often hand this most decisive of gifts—to be present and yet unseen—to the errand-runner of the gods and to the crown of the dead?