The story of Prometheus being chained to a mountain to have his liver eaten by an eagle everyday because he is punished by Zeus for giving man fire, until he is rescued by Heracles, is symbolic of a flood that occurred in Egypt that wrecked the Egyptian lands of Prometheus and the help Heracles gave to stop the flooding waters from destroying his land. Here is what was written by Diodorus Siculus in his Library of History:
While Osiris and his army were thus employed, the Nile, they say, at the time of the rising of Sirius, which is the season when the river is usually at flood, breaking out of its banks inundated a large section of Egypt and covered especially that part where Prometheus was governor; and since practically everything in the district was destroyed, Prometheus was so grieved that he was on the point of quitting life willfully. Because its water sweeps down so swiftly and with such violence the river was given the name Aetus; but Heracles being ever intent upon great enterprises and eager for the reputation of a manly spirit, speedily stopped the flood at its breach and turned the river back into its former course. Consequently certain of the Greek poets worked the incident into a myth, to with effect that Heracles had killed the eagle which was devouring the liver of Prometheus. (page 60-61, volume 1).
As often is the case, many of the myths have symbolism associated with them to allow a true part of the past to be remembered. As an interpreter and researcher of mythology, I try to uncover the truth in the myths and have shown through my Mythological Unification Theory the story of this ancient family and their trials and triumphs. Each one of the family members was associated with a part of the Earth, a star system, an element, or some sacred animal or object. For example, when the sky rained or thundered, it was associated with the will of Zeus since he was associated with the sky in the cosmology invented by this ancient family from Crete and Tyre.