The earliest form of under-water attack was carried out by divers long before explosive compounds were invented, and the old writers have strange stories to tell of fierce fights beneath the waves. “The first divers learned their art,” says John Beckmann, in his “History of Inventions and Discoveries,” “by early and adventurous experience, in trying to continue under water as long as possible without breathing, and indeed it must be allowed that some of them carried it to very great perfection. This art, however, excites little surprise, for, like running, throwing, and other bodily dexterities, it requires only practice; but it is certain that those nations called by us uncultivated and savage excel in it the Europeans who through refinement and luxury have become more delicate and less fit for such laborious exercises.” In early times divers were employed for peaceful as well as for hostile purposes. They were kept in ships to assist in raising anchors and to recover goods thrown overboard in times of danger, and by the laws of the Rhodians they were allowed a share of the wreck, proportional to the depth at which they had gone in search of it. “The pearls of the Greek and Roman ladies,” writes Beckmann, “were fished up by divers at the great hazard of their lives, and by the like means are procured at present those which are purchased as ornaments by our fair.” In the operations of war divers were used for many purposes. Beckmann tells us that when Alexander was besieging Tyre, divers swam off from the city under water to a great distance and with long hooks tore to pieces the mole with which the besiegers were endeavouring to block up the harbour. We learn from Herodotus (viii. 8) that when the fleet of Xerxes was advancing to the invasion of Greece, “there was in the force one Skyllias, a Skionaian, the best diver of his time, who in the shipwreck off Pilîon had saved many things for the Persians and had also obtained many things himself.” This diver deserted to the Greeks and gave them the benefit of his skill as well as of recent intelligence concerning their enemy. He was the means of destroying a number of the Persian ships by a curious kind of submarine attack. Accompanied by his daughter Kyane, whom he had instructed in his art, he dived during a storm and “cast off” the cables from the anchors which held the vessels, the result being that they were driven on shore and wrecked. Thucydides (iv. 26) gives an instance of a case of divers being employed as subaqueous auxiliaries during the siege of Syracuse.