Hades possesses a helmet—which the CYCLOPES gave him (as they also gave the thunderbolt to Zeus and the trident to Poseidon)—that rends the wearer invisible. He sometimes lends it to both gods and men: for example, Perseus 1 put the helmet on his head when he went to kill Medusa, and Hermes, wearing the helmet, fought the GIANTS. Later Athena, during the Trojan War, put on the helmet of Hades so that Ares should not see her (see Diomedes).
With this she caught hold of Sthenelus and lifted him off the chariot on to the ground. In a second he was on the ground, whereupon the goddess mounted the car and placed herself by the side of Diomed. The oaken axle groaned aloud under the burden of the awful goddess and the hero; Pallas Minerva took the whip and reins, and drove straight at Mars. He was in the act of stripping huge Periphas, son of Ochesius and bravest of the Aetolians. Bloody Mars was stripping him of his armour, and Minerva donned the helmet of Hades, that he might not see her; when, therefore, he saw Diomed, he made straight for him and let Periphas lie where he had fallen. As soon as they were at close quarters he let fly with his bronze spear over the reins and yoke, thinking to take Diomed's life, but Minerva caught the spear in her hand and made it fly harmlessly over the chariot. Diomed then threw, and Pallas Minerva drove the spear into the pit of Mars's stomach where his under-girdle went round him. There Diomed wounded him, tearing his fair flesh and then drawing his spear out again. Mars roared as loudly as nine or ten thousand men in the thick of a fight, and the Achaeans and Trojans were struck with panic, so terrible was the cry he raised.