When Alexander threw some parts of India into a commotion and took possession of others he encountered among many other animals a Serpent which lived in a cavern and was regarded as sacred by the Indians who paid it great and superstitious reverence. Accordingly Indians went to all lengths imploring Alexander to permit nobody to attack the Serpent; and he assented to their wish. Now as the army passed by the cavern and caused a noise, the Serpent was aware of it. (It has, you know, the sharpest hearing and the keenest sight of all animals.) And it hissed and snorted so violently that all were terrified and confounded. It was reported to measure 70 cubits although it was not visible in all its length, for it only put its head out. At any rate its eyes are said to have been the size of a large, round Macedonian shield.
Aelianus, Claudius, On Animals, Book #XV, Chapter 19-23, c.210-230.