During the siege a Syrian architect named Callinicus is said to have come to Constantinople with a preparation of his own invention, "Greek fire," which he offered the Emperor for use against the Saracen. This, according to one historian, "was a semi-liquid substance, composed of sulphur, pitch, dissolved niter, and petroleum boiled together and mixed with certain less important and more obscure substances.... When ejected it caught the woodwork which it fell and set it so thoroughly on fire that there was no possibility of extinguishing the conflagration. It could only be put out, it is said, by pouring vinegar, wine, or sand upon it."[1] [Footnote 1: THE ART OF WAR, Oman, p. 546.] Constantine IV, the Emperor, was quick to see the possibilities of the innovation and equipped his dromons with projecting brass tubes for squirting the substance upon the enemy's ships. These are sometimes referred to as "siphons," but it is not clear just how they were operated. One writer[2] is of the opinion that something of the secret of gunpowder had been obtained from the East and that the substance was actually projected by a charge of gunpowder; in short, that these "siphons" were primitive cannon. In addition to these tubes other means were prepared for throwing the fire. Earthenware jars containing it were to be flung by hand or arbalist, and darts and arrows were wrapped with tow soaked in the substance. [Footnote 2: THE BYZANTINE EMPIRE, Foord, p. 139.] The Christian fleet was no match for the Saracen in numbers, but Constantine pinned his faith on the new invention. Accordingly, during the fourth year of the siege, 677, he boldly led his fleet to the attack. We have no details of this battle beyond the fact that the Greek fire struck such terror by its destructive effect that the Saracens were utterly defeated. This unexpected blow completed the growing demoralization of the besiegers. The army returned to the Asiatic shore of the Bosphorus, and the survivors of the fleet turned homewards. Constantine followed up his victory with splendid energy. He landed troops on the Asiatic shore, pursued the retreating Arabs and drove the shattered remnant of their army back into Syria. The fleet was overtaken by a storm in the AEgean and suffered heavily. Before the ships could reassemble, the Christians were upon them and almost nothing was left of the great Saracen armada. Thus the second great assault on Constantinople was shattered by the most staggering disaster that had ever befallen the cause of Islam. The Christian empire once more stood supreme, and that supremacy was attested by the terms of peace which the defeated Muaviah was glad to accept. There was to be a truce of thirty years, during which the Christian emperor was to receive an annual tribute of 3000 pounds of gold, fifty Arab horses and fifty slaves.