Briareus mother Gaia
In Greek mythology, the Hecatoncheires (Greek: Ἑκατόγχειρες, lit. "Hundred-Handed Ones"), or Hundred-Handers, also called the Centimanes (; Latin: Centimani), named Cottus, Briareus (or Aegaeon) and Gyges (or Gyes), were three monstrous giants, of enormous size and strength, each with fifty heads and one hundred arms.  In the standard tradition they were the offspring of Uranus (Sky) and of Gaia (Earth), and helped Zeus and the  Olympians to overthrow the Titans in the Titanomachy.Mythology
The Hundred-Handers
The Hundred-Handers, Cottus, Briareus and Gyges, were three monstrous giants, of enormous size and strength, with fifty heads and one hundred arms. They were among the eighteen offspring of Uranus (Sky) and Gaia (Earth), which also included the twelve Titans, and the three one-eyed Cyclopes. According to the Theogony of Hesiod, they were the last of these children of Uranus to be born, while according to the mythographer Apollodorus they were the first. In the Hesiodic tradition, they played a key role in the Greek succession myth, which told how the Titan Cronus overthrew his father Uranus, and how in turn Zeus overthrew Cronus and his fellow Titans, and how Zeus was eventually established as the final and permanent ruler of the cosmos.According to the standard version of the succession myth, given in the accounts of Hesiod and Apollodorus, the Hundred-Handers, along with their brothers the Cyclopes, were imprisoned by their father Uranus. Gaia induced Cronus to castrate Uranus, and Cronus took over the supremacy of the cosmos. With his sister the Titaness Rhea, Cronus fathered several offspring, but he swallowed each of them at birth. However, Cronus' last child Zeus was saved by Rhea, and Zeus freed his brothers and sisters, and together they (the Olympians) began a great war, the Titanomachy, against the Titans, for control of the cosmos. Gaia had foretold that, with the help of the Hundred-Handers, the Olympians would be victorious, so Zeus released them from their captivity and the Hundred-Handers fought alongside the Olympians against the Titans and were instrumental in the Titans' defeat. The Titans were then imprisoned in Tartarus with the Hundred-Handers as their guards.The lost epic poem the Titanomachy (see below), although probably written after Hesiod's Theogony, perhaps preserved an older tradition in which the Hundred-Handers fought on the side of the Titans, rather than the Olympians. According to a euhemeristic rationalized account, given by Palaephatus,  Cottus and Briareus, rather than being hundred-handed giants, were instead men, who were called the Hundred-Handers because they lived in a city called Hecatoncheiria ("Hundredarm"). They came to the aid of the residents of the city of Olympia (i.e. the Olympians) in driving away the Titans from their city.Titan ally
While in Hesiod and Homer, the powerful Hundred-Hander Briareus was a faithful and rewarded ally of Zeus, the Titanomachy seems to have reflected a different tradition. Apparently, according to the Titanomachy, Aegaeon was the son of Gaia and Pontus (Sea), rather than Gaia and Uranus, and fought on the side of the Titans, rather than the Olympians. The scholiast on  Apollonius of Rhodes, tells us that according to Cinaethon, Aegeaon was defeated by Poseidon. Apollonius of Rhodes mentions the "great tomb of Aegaeon", seen by the Argonauts when "they were passing within sight of the mouth of the Rhyndacus ... a short distance beyond Phrygia". The scholiast on Apollonius, says that the tomb marked the spot where Aegaeon's defeat occurred.As in the lost Titanomachy, for the Latin poets Virgil and Ovid, Briareus was also an enemy of the gods, rather than an ally.  In his Aeneid, Virgil has Aegaeon make war against the gods, "with fifty sounding shields and fifty swords". Ovid, in his poem Fasti, has Briareus on the side of the Titans. As Ovid tells us, after the Titans had been overthrown, apparently in order to restore the Titans to power, Briareus sacrificed a bull, about which it had been prophesied that whoever burned its entrails would be able to conquer the gods. However just when Briareus was about to burn the entrails, birds snatched them away, and were rewarded with a home among the stars.Principal sources
The Theogony
According to the Theogony of  Hesiod, Uranus (Sky) mated with Gaia (Earth) and produced eighteen children.  First came the twelve Titans, next the three one-eyed Cyclopes, and finally the three monstrous brothers Cottus, Briareus and Gyges. As the Theogony describes it:Eumelus in the Titanomachy says that Aigaion was the son of Earth and Sea, lived in the sea, and fought on the side of the Titans.
Thus the  Titanomachy apparently followed a different tradition than the more familiar account in the Theogony. Here Briareus/Aegaeon was the son of Earth (Gaia) and Sea (Pontus) rather than Earth and Sky (Uranus), and he fought against the Olympians, rather than for them.
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