There is much obscurity about the invention of gunpowder. It is usually supposed to have been invented in China, and to have crept its way first to the western Asian nations, and afterwards to Europe by way of the Mediterranean. There can be little doubt that gunpowder was known to the Romans in the days of the empire; and some accounts of Alexander's campaigns declare that he used mines to destroy the walls of Gaza. It is supposed by many that the Chinese had cannon, from certain embrasures in some of their ancient walls; but there seems to be no absolute proof of this. It seems fairly well established that the Moors used artillery in Spain in the twelfth century; though some writers hold that what were called firearms in Europe before the fourteenth century were only engines which threw fire into besieged places. It seems probable that the gun was invented as the result of an accident that occurred while some man was pounding the (gunpowder) mixture of charcoal, saltpetre and sulphur in a receptacle of some kind. According to one story, the mixture exploded and threw the pestle violently out of the mortar. From this incident, the man who was handling the pestle, or a bystander, is supposed to have conceived the idea that the powder could be used intentionally to throw projectiles, and he is supposed also to have actually proved that it could be done at will, and to have produced a concrete appliance for doing it. From the history of the case, it would seem that the first gun was what we still call a "mortar." It may occur to some that (conceding the story to be true, which it possibly is, in essentials) the gun was not an invention so much as a discovery. It may be pointed out, however, that while the fact that gunpowder would blow a pestle out of a mortar might be truly called a discovery, yet the conception of utilizing the discovery by making a weapon, and the subsequent making of the weapon constituted an invention of the most clean-cut kind.