The Titans of Greek Mythology were the offspring of Uranus, god of heaven, and Gaea, goddess of the earth. Uranus and Gaea had twelve children, six sons and six daughters. These twelve themselves had children, and some of them are known to us as Titans, such as Prometheus and Atlas. The Titan Cronos fathered those we now know as Olympian gods. Olympus, being the highest mountain in Greece, with its imposing summit, was believed by the ancient Greeks to be the abode of Zeus and the entire Greek pantheon of gods.
Uranus hated and loathed his offspring, and jealously banished these Cyclopes and Hecatoncheire to the underworld. Gaea was deeply grieved by this treatment, and instigated her son Cronos to lead the Titans in an uprising. Under Cronos' leadership the Titans rebelled against the cruel Uranus. However, once Cronos had replaced his father as supreme ruler, he proved to be a despot himself and failing to uphold justice, he and his loyal Titans imprisoned his brethren Cyclopes and Hecatoncheire once again in the underworld.
Upon reaching maturity, Zeus waged war against his father Cronos and the Titans. Led by Zeus, the gods fought from Mount Olympus against the Titans who fought from Mount Othrys. A ten year war waged, with no end in sight. It was at this time that Rhea prophesied the victory of Zeus if he would unchain the Cyclopes and Hecatoncheire from their underworld imprisonment of Tartarus. The one-eyed Cyclopes named Brontes, Arges, and Steropes were powerful fighters and masterful armorers. The Hecatoncheires named Briareus, Cottus, and Gyges had a hundred hands and were stronger and more fierce than even the mighty Cyclopes. Upon slaying their captor and freeing them, Zeus revived the Hecatoncheire and Cyclopes with nectar and ambrosia. In return, the Cyclopes bestowed upon Zeus the mighty lightning bolts, upon Poseidon they bestowed a powerful trident, and upon Hades they placed an implacable helmet of invisibility. The Hecatoncheire for their part wielded great stones in their hundred arms, and so armed, Zeus and the Olympian gods made war upon Cronos and the Titans loyal to him. The sky was filled with thunderbolts and hundreds of great stones, as the Olympians smote and deposed Cronos from his throne.
Having thus defeated Cronos, the Olympian gods cast lots for who would rule the world. Zeus for his part was given the skies, Poseidon was given the seas, and to Hades was granted dominion of the Underworld. The Titans were chained in the underworld prison Tartarus that once housed their brethren. The mighty Hecatoncheire were charged with their guard, and so the former prisoners became jailers of evil.
This war between the TITANS and the OLYMPIANS is known as the Titanomachy.
-- Greek Mythology of "WAR OF TITANS"