Eurystheus hid in a bronze jar when Hercules returned with Cerberus.
The final labor required Hercules to bring Cerberus, the guard dog of the underworld, to the surface world. When Hercules presented the terrifying creature to Eurystheus, the king was so frightened that he concealed himself in a large bronze vessel, commonly described as a jar or pithos.
The image emphasizes the contrast between the two men. Hercules had entered the underworld and subdued its guardian, while Eurystheus, who had assigned the task, could not face the result. Some retellings call the vessel a bronze jar, while artistic and literary translations may use “jar,” “pithos,” or “urn.”
After Eurystheus had seen Cerberus, Hercules returned the hound to the underworld. The dog therefore did not become a permanent possession of the hero or remain in the human world. The bronze jar is a detail of Eurystheus’ reaction, not a separate labor.