Isaac Asimov's Worlds of Fantasy. Book 6: Mythical Beasties

Pegascis

One of the most enduring dreams of human beings is to fly. Ail sorts of spirits and monsters were pictured with wings, since flying seemed an obvious attribute of supernatural beings. In addition, there were various ways of enabling human beings toffy-flying carpets, for instance, are common in the stories included in The Arabian Nights."

The ancient Greeks came up with the most attractive of all flying creatures-Pegasus, the divine and immortal winged horse. The thought of a flying horse may well have arisen from the wonder of horseless human beings at the speed with which a horseman could cover the ground. To a man going no faster than an oxcart will carry him, the racing horse might as well have been flying.

Pegasus was supposed to have been born of the blood of the severed head of Medusa, the gorgon killed by the Greek hero Perseus. Another Greek hero, Bellerophon, rode Pegasus during the task of killing the chimera, and later in wars against the Amazons. Still later, Bellerophon tried to use Pegasus to scale Olympus, the home of the gods, but was thrown and badly hurt as punishment for this blasphemous attempt.

In later myths, Pegasus was associated with poetic inspiration. After all, the poet's fancy lifts him to the skies (so to speak) as though he were riding a flying horse. Pegasus was supposed to have landed on Mount Helicon near Thebes, and his hoof dug out a hollow from which emerged a spring called the Hippocrene (''fountain of the horse"). which was a legendary source of poetic inspiration.

It's almost a shame to have to point out that musclepowered wings could not support the weight of a man, let alone that of a horse. The following story, however, tackles that impossibility.