The Greek Fire

 A description of the Greek Fire according to Edward Gibbon in his The History of the Decline and Fall of the Roman Empire, chapter LII.

In the two sieges [by the Saracens], the deliverance of Constantinople may be chiefly ascribed to the novelty, the terrors, and the real efficacy of the Greek fire. The important secret of compounding and directing this artificial flame was imparted by Callinicus, a native of Heliopolis in Syria, who deserted from the service of the caliph to that of the emperor.  The skill of a chemist and engineer was equivalent to the succor of fleets and armies; and this discovery or improvement of the military art was fortunately reserved for the distressful period, when the degenerate Romans of the East were incapable of contending with the warlike enthusiasm and youthful vigor of the Saracens.
The historian who presumes to analyze this extraordinary composition should suspect his own ignorance and that of his Byzantine guides, so prone to the marvellous, so careless, and, in this instance, so jealous of the truth. From their obscure, and perhaps fallacious, hints it should seem that the principal ingredient of the Greek fire was the naphtha,  or liquid bitumen, a light, tenacious, and inflammable oil,  which springs from the earth, and catches fire as soon as it comes in contact with the air. The naphtha was mingled, I know not by what methods or in what proportions, with sulphur and with the pitch that is extracted from evergreen firs.  From this mixture, which produced a thick smoke and a loud explosion, proceeded a fierce and obstinate flame, which not only rose in perpendicular ascent, but likewise burnt with equal vehemence in descent or lateral progress; instead of being extinguished, it was nourished and quickened by the element of water; and sand, urine, or vinegar, were the only remedies that could damp the fury of this powerful agent, which was justly denominated by the Greeks the liquid, or the maritime, fire.
For the annoyance of the enemy, it was employed with equal effect, by sea and land, in battles or in sieges. It was either poured from the rampart in large boilers, or launched in red-hot balls of stone and iron, or darted in arrows and javelins, twisted round with flax and tow, which had deeply imbibed the inflammable oil; sometimes it was deposited in fire-ships, the victims and instruments of a more ample revenge, and was most commonly blown through long tubes of copper which were planted on the prow of a galley, and fancifully shaped into the mouths of savage monsters, that seemed to vomit a stream of liquid and consuming fire. This important art was preserved at Constantinople, as the palladium of the state: the galleys and artillery might occasionally be lent to the allies of Rome; but the composition of the Greek fire was concealed with the most jealous scruple, and the terror of the enemies was increased and prolonged by their ignorance and surprise. In the treaties of the administration of the empire, the royal author suggests the answers and excuses that might best elude the indiscreet curiosity and importunate demands of the Barbarians. They should be told that the mystery of the Greek fire had been revealed by an angel to the first and greatest of the Constantines, with a sacred injunction, that this gift of Heaven, this peculiar blessing of the Romans, should never be communicated to any foreign nation; that the prince and the subject were alike bound to religious silence under the temporal and spiritual penalties of treason and sacrilege; and that the impious attempt would provoke the sudden and supernatural vengeance of the God of the Christians. By these precautions, the secret was confined, above four hundred years, to the Romans of the East; and at the end of the eleventh century, the Pisans, to whom every sea and every art were familiar, suffered the effects, without understanding the composition, of the Greek fire. It was at length either discovered or stolen by the Mahometans; and, in the holy wars of Syria and Egypt, they retorted an invention, contrived against themselves, on the heads of the Christians. A knight, who despised the swords and lances of the Saracens, relates, with heartfelt sincerity, his own fears, and those of his companions, at the sight and sound of the mischievous engine that discharged a torrent of the Greek fire, the feu Gregeois, as it is styled by the more early of the French writers. It came flying through the air, says Joinville, 22 like a winged long-tailed dragon, about the thickness of a hogshead, with the report of thunder and the velocity of lightning; and the darkness of the night was dispelled by this deadly illumination. The use of the Greek, or, as it might now be called, of the Saracen fire, was continued to the middle of the fourteenth century, 23 when the scientific or casual compound of nitre, sulphur, and charcoal, effected a new revolution in the art of war and the history of mankind