The earth is naturally full of cavities, containing much empty 1 space. Through these cavities air roams. When an excessive quantity has entered and cannot escape it shakes the earth. This explanation is approved by others, too, as mentioned a little above. Perhaps the crowd of witnesses will impress you. The view has the adhesion of Callisthenes, and he is a man not lightly to be set aside. He was endowed with a lofty intellect, and he dared to brave the wrath of a king. His death is an eternal blot on the memory of Alexander, which no valour and no success in war can ever remove. As often as it is said, Alexander slew many thousands of the Persians, the retort will 2 be, And Callisthenes too. As often as it is said, He slew Darius, in whose hands there was then a mighty kingdom, the retort will be, Yes, and Callisthenes too. As often as it is said, He conquered all lands right up to the Ocean, the Ocean likewise he essayed with fleets strange to its waters, from a corner of Thrace he extended his empire to the bounds of the East; it will also be said, Yes, but he slew Callisthenes. Granted that he surpassed all former precedents of 3 generals and kings, yet of all that he did, nothing will match his guilt in slaying Callisthenes. Well, this Callisthenes, in the treatise in which he gives details of the sinking of Helice and Buris, and discusses the disaster which sent them into the sea, or the sea into them, says what I have said at a previous point. Air, he says, enters the earth by hidden openings under the sea, just as everywhere else. By and by, when the path is 4 blocked by which it had descended, and the resistance of the water in the rear has cut off its retreat, it is borne hither and thither, and encountering itself in its course it undermines the earth. That is the reason why land over against the sea is most frequently harassed by earthquakes; and hence it is that Neptune has been assigned this power of moving the earth.[85] Any one who has learned the elements of Greek knows that he is called among the Greeks Earthshaker (Ἐνοσίχθων). [85] The usual reading, _maris_ = sea, contradicts the argument; it cannot surely be right. XXIV