Of the vultures, the black ones2912 are the strongest. No person has yet found a vulture’s nest: hence it is that there are some who have thought, though erroneously, that these birds come from the opposite hemisphere.2913 The fact is, that they build their nest upon the very highest rocks; their young ones, indeed, are often to be seen, being generally two in number. Umbricius, the most skilful among the aruspices of our time, says that the vulture lays thirteen eggs,2914 and that with one of these eggs2915 it purifies the others and its nest, and then throws it away: he states also that they hover about for three2916 days, over the spot where carcases are about to be found.