Zeus freed the Cyclopes and Hecatoncheires to help the Olympians defeat the Titans.
In Greek succession mythology, Uranus had imprisoned these beings beneath the earth or in Tartarus. The Cyclopes were one-eyed divine smiths, while the Hecatoncheires—Cottus, Briareus, and Gyges—were giants with fifty heads and one hundred arms.
After Zeus forced Cronus to disgorge his swallowed siblings, he released the prisoners. In Apollodorus’s version, Zeus first killed their guard, Campe. The Cyclopes rewarded him with thunderbolts, while the Hecatoncheires used their immense strength to hurl boulders at the Titans.
A common mix-up is confusing Zeus’s liberation with Cronus’s earlier overthrow of Uranus. Cronus freed some imprisoned beings during his revolt but then confined the Cyclopes and Hecatoncheires again. Zeus’s release was the one that directly aided the Olympian victory. The Titanomachy traditionally lasted ten years.