Some writers add to the above a seventh kind, which they call the “bearded”[2905] eagle; the Tuscans, however, call it the ossifrage. CHAP. 4.—THE NATURAL CHARACTERISTICS OF THE EAGLE. The first three and the fifth class of eagles employ in the construction of their aerie the stone aëtites,[2906] by some known as “gangites;” which is employed also for many remedial purposes, and is proof against the action of fire. This stone has the quality also, in a manner, of being pregnant, for when shaken, another stone is heard to rattle within, just as though it were enclosed in its womb; it has no medical properties, however, except immediately after it has been taken from the nest. Eagles build among rocks and trees; they lay three eggs, and generally hatch but two young ones, though occasionally as many as three have been seen. Being weary of the trouble of rearing both, they drive one of them from the nest: for just at this time the providential foresight of Nature has denied them a sufficiency of food, thereby using due precaution that the young of all the other animals should not become their prey. During this period, also, their talons become reversed, and their feathers grow white from continued hunger, so that it is not to be wondered at that they take a dislike to their young. The ossifrage, however, a kindred species, takes charge of the young ones thus rejected, and rears them with its own; but the parent bird still pursues them with hostility, even when grown up, and drives them away, as being its rivals in rapine. And indeed, under any circumstances, one pair of eagles requires a very considerable space of ground to forage over, in order to find sufficient sustenance; for which reason it is that they mark out by boundaries their respective allotments, and seek their prey in succession to one another. They do not immediately carry off their prey, but first deposit it on the ground, and it is only after they have tested its weight that they fly away with it. They die, not of old age, nor yet of sickness, or of hunger; but the upper part of the beak grows to such an extent, and becomes so curved, that they are unable to open it. They take the wing, and begin upon the labours of the chase at mid-day; sitting in idleness during the hours of the morning, until such time as the places[2907] of public resort are filled with people. The feathers of the eagle, if mixed with those of other birds, will consume them.[2908] It is said that this is the only bird that has never been killed by lightning; hence it is, that usage has pronounced it to be the armour-bearer of Jove. CHAP. 5. (4.)—WHEN THE EAGLE WAS FIRST USED AS THE STANDARD OF THE ROMAN LEGIONS.