Geryon was a monster, born from parents who were also fierce creatures, and the grandson of Medusa (who had snakes for hair, and any hiuman who looked directly at her would be turned to stone). It was no surprise that Geryon was a wicked-looking giant – many stories say he had three bodies, three heads, or six legs. Geryon owned some red cattle, which were guarded by Orthrus, a fierce two-headed dog, and the herder Eurytion.
Before Heracles even met Geryon, first he had to get there. To do this he had to kill many beasts, and also build two mountains. Finally, he crossed a desert where, angry with the heat, he shot an arrow at Helios, the Sun. The Sun, thinking Heracles quite brave for trying to fight such a great being, gave him a golden cup which it used to sail across the waters from east to west each day, and so Heracles used this to travel rather than in the desert.
Capturing the cattle was actually a quick labor for Heracles – when Orthrus arrived Heracles simply hit it with a club, and then killed Eurytion. Another herder quickly told Geryon what was happening, and he ran to fight Heracles; Heracles, however, simple shot the giant with one of the arrows covered in the poison of the Hydra.
The real problems, however, then began. The cattle were not easy to control, and one night as Heracles was sleeping the giant Cacus stole some of the cattle, making them walk backwards so Heracles would not know which way they had been taken. Some stories say the stolen cattle called the others, allowing Heracles to find them, whilst others say Cacus’s sister simply told him where they were; either way Heracles found them, killed Cacus, and returned to the herd.
At Rhegiem another problem occured: a bull escaped and jumped into the sea. It was found by Eryx, a son of Poseidon (god of the sea), and put into Eryx’s own herd. When Heracles finally found the bull he asked for it back, but Eryx said he would only do this if Heracles could beat him in a wrestling match. The two fought three times, each time with heracles winning. In the end Heracles killed Eryx, and took his bull back (the word ‘italus’ meant bull, and it is from this story that the country Italia (Italy) gets its name).
The next problem came at the shores of the Ionian Sea: Hera, still angry with Heracles, sent a gadfly to bite and annoy the cattle. It worked, and soon the cattle were running in every direction. it took Heracles a great deal of time to regroup the animals and when he did, thinking the problem had been because of the River Strymon (not Hera) Heracles filled the entire river with stones.
Finally, after a year, Heracles returned to King Eurystheus, and the cattle were sacrificed to please Hera.

The ten tasks had taken 8 years and one month, but Heracles was not yet a free man: King Eurystheus declared that both the Lernaean Hydra (because his nephew Iolaus had helped by handing him the fire) and the Augean Stables (because he had used a river) did not count. Two more labors needed to be done.