Before their birth, the coming of the twins was fortold. They were sons of Poseidon, and could not be killed by either God or man. Mighty Zeus' thunderbolts were useless, as was Heracles' strength. As the boys grew into giants they learned arrogance and the anger that comes from invulnerability. Ephialtes decided that he desired the Goddess Hera, and spent long evenings invisioning how he would dominate and violate the proudest and noblest of the Goddesses. Otus preferred Artemis, the Virgin Lady of Wild Things, for his rape subject. He would do what no other could. They had great strength and mighty issues, did this pair. Rightly, the twins discounted the brute strength of the Gods. They were male, and looked only to the male strength as a threat. The female power - that of wit - was never considered.
So Otus and Ephialtes set off for Olympus, planning to crush the Gods before them and set themselves up as the new rulers of the world. During their seige they locked up Ares in a little bronze jar for 13 months. They had taken over Olympus soon, and there appeared to be no hope for the Olympians. During a break in the battle, Otus and Ephialtes called for Hera and Artemis repeatedly. Time after time they were refused, until at last, miraculously, the Goddesses accepted. Or rather, Artemis did. Hera still refused vehemently. Artemis went to Otus, and said if he would let out Ares, he could do with her what he would. Otus was ecstatic, but Ephialtes wasn't too happy. The brothers began to quarrel, and when they weren't looking Artemis turned into a deer. When the fighting reached a peak, she sprang between them as a white doe. Both men broke off and threw their spears at the lovely creature, but they were so distracted, and she was so fast, that the spears missed. Not only did they miss, but Artemis had set them up so that when they threw what was actually impaled was the brothers.
Otus and Ephialtes accomplished what none of the Gods could do, they killed each other.
Artemis returned to Olympus a heroine. Hera retained her dignity. Ares . . . well, Ares they left in the jar a little longer. No one liked him very much.