The concept of doing something "under someone's aegis" means doing something under protection of a powerful, knowledgeable, or benevolent source. The word aegis is identified with protection by a strong force with its roots in Greek mythology, adopted by the Romans; there are parallels in Norse mythology, and in Egyptian mythology as well, where the Greek word aegis is applied by extension.
The aegis (Greek Αιγίς), already attested in the Iliad, is the shield or buckler of Zeus or of Pallas Athena, which according to Homer was fashioned by Hephaestus, furnished with golden tassels and bearing the Gorgoneion (Medusa's head) in the central boss. Some of the Attic vase-painters retained an archaic tradition that the tassels had originally been serpents in their representations of the ægis.
When the Olympian shakes the aegis, Mount Ida is wrapped in clouds, the thunder rolls and men are struck down with fear. "Aegis-bearing Zeus", as he is in the Iliad, sometimes lends the fearsome goatskin to Athena. In the Iliad when Zeus sends Apollo to revive the wounded Hector of Troy, Apollo, holding the aegis, charges the Achaeans, pushing them back to their ships drawn up on the shore. According to Edith Hamilton's Mythology: Timeless Tales of Gods and Heroes , the Aegis is Zeus' breastplate, and was "awful to behold."
There is also the origin myth that represents the ægis as a fire-breathing chthonic monster similar to the Chimera, which was slain and flayed by Athena, who afterwards wore its skin as a cuirass (Diodorus Siculus iii. 70), or as a chlamys. The Douris cup shows that the aegis was represented exactly as the skin of the guardian serpent, with its scales clearly delineated.
In a late rendering by Hyginus, (Poetical Astronomy ii. 13) Zeus is said to have used the skin of the goat Amalthea (aigis "goat-skin") which suckled him in Crete, as a shield when he went forth to do battle against the titans.
It often is represented on the statues of Roman emperors, heroes, and warriors as well as on cameos and vases. A vestige of that appears in a portrait of Alexander the Great in a fresco from Pompeii dated to the first century B.C., which shows the image of the head of a woman on his armor that resembles the Gorgon.
Robert Graves in The Greek Myths (1955; 1960) asserts that the ægis in its Libyan sense had been a shamanic pouch containing various ritual objects, bearing the device of a monstrous serpent-haired visage with tusk-like teeth and a protruding tongue which was meant to frighten away the uninitiated. In this context, Graves identifies the aegis as clearly belonging first to Athena.
Another version describes it to have been really the goat's skin used as a belt to support the shield. When so used it would generally be fastened on the right shoulder, and would partially envelop the chest as it passed obliquely round in front and behind to be attached to the shield under the left arm. Hence, by metonymy, it would be employed to denote at times the shield which it supported, and at other times a cuirass, or chlamys , the purpose of which it in part served. In accordance with this double meaning, the ægis appears in works of art sometimes as an animal's skin thrown over the shoulders and arms, and sometimes as a cuirass, with a border of snakes corresponding to the tassels of Homer, usually with the Gorgon's head, the gorgoneion, in the centre. It is often represented on the statues of Roman emperors, heroes, and warriors, and on cameos and vases.
A current modern interpretation is that the Hittite sacral hieratic hunting bag (kursas), a rough and shaggy goatskin that has been firmly established in literary texts and iconography by H.G. Güterbock, is the most likely source of the aegis..
The original meaning may have been #1, and Ζευς 'Αιγιοχος = "Zeus who holds the aegis" may have originally meant "Sky/Heaven, who holds the storm". The transition to the meaning "shield" may have come by folk-etymology among a people familiar with draping an animal skin over the left arm as a shield.
Ancient Nubia shared many aspects of its mythology with ancient Egypt and there is debate about the original source of some religious concepts that the two cultures share and, whether the assimilation was from Nubia to Egypt, the reverse, or through continuing exchanges. At one time the Kush of Nubia ruled ancient Egypt.
The image to the right was discovered in Sudan, which is the contemporary name for the territory of Nubia during the period in which the artifact was made, during the 300s BC. The figure is that of Isis and she is wearing an aegis. It is likely to be an artifact of the flourishing culture of Meroë, successors to the culture of Kush, because of the use of Egyptian hieroglyphs and cartouches.