Definition of "ægis"

Herodotus, as proof of this origin of Minerva, says, that the Greeks had taken from the Libyan women, the dress and the ægis with which her statues were represented: this dress was of leather: the ægis, as its name implies, was simply a goatskin died red and worn over the shoulders like a mantle: the extremity of it was cut into shreds or tassels, which the lively fancy of the Grecian artists converted into serpents.

1822, James Millingen, Painted Greek Vases, from Collections in Various Countries: […] (Ancient Unedited Monuments; series 1), London: [s.n.], page 3

[T]hree ex-Secretaries of State for War had learnt their military theory under the ægis of Regular soldiers. Now it is an admitted fact that, broad-minded and enterprising as soldiers have frequently proved themselves in matters unconnected with the actual corporate body to which they belong, they are, nevertheless, perhaps the most obstinate and optimistic advocates of a laissez-faire policy, which the interests of their own profession are at issue, that it is at all possible to conceive.

1913 March, “National Safety (II): The Real Obstacle to Military Reform”, in The Nineteenth Century and After: A Monthly Review Founded by James Knowles, volume LXXIII, number CCCCXXXIII, New York, N.Y.: Leonard Scott Publication Co.; London: Spottiswoode & Co. Ltd., printers, page 490