Projectile-throwing machines were developed after the fashion of a crossbow mounted upon a small wooden carriage which usually was a hollowed trough open on top and upon which a stone was laid. The thong of the crossbow was drawn by a powerful screw operated by man power, and the crossbow arrangement when released would throw a stone weighing many pounds quite a distance over the walls of a besieged city or from such wall into the camps or ranks of the besiegers. This again was an attempt by mechanical means to develop and strengthen and lengthen the stroke of the arm and the weight of the projectile. The Bible states that King Usia (809-757 B. C.) placed types of artillery on the walls of Jerusalem. The Romans used it in the Punic Wars. The Alexandrian technicians established scientific rules for the construction of early weapons. Athenaeus reports catapults having a range of 656 meters and that the gigantic siege tower at Rhodes successfully resisted stone projectiles weighing 176 pounds. References to explosives are to be found in works as old as Moses. Archimedes is said by Plutarch to have “cast huge stones from his machines with a great noise;” Caligua is said by Dion Cassius to have had machines which “imitated thunder and lightning and emitted stones;” and Marcus Graecus in the eighth century gives a receipt of one pound of sulphur, two of willow charcoal and six of saltpetre, for the discharge of what we should call a rocket. The use of Greek fire was understood as early as the sixth century, but powder was earliest used in China, perhaps a thousand years before Christ, and was introduced to European notice by the Saracens. From the discovery of gunpowder by the English monk Bacon in 1248, sixty-five years elapsed before a Franciscan monk produced the first gun in Germany, about 1313. The first guns were of a small breech-loading type, supported in front by crossed sticks and anchored by a spike at the breech. Later these guns were fastened to cradles, the latter being mounted on sleighs, and finally, in 1376, the Venetians produced the first wheel mounts, which had become common by 1453, when the Turks took Constantinople. The ancient carriages were remarkable because of the fact that in general design they embodied the same principals which are included in the field carriages of to-day. One example from the fifteenth century shows a breech-loading gun mounted in a cradle supported by trunnions on the forward extension of the trail over the axle. The cradle was elevated by a pin-and-arc arrangement, supported on the trail. The axle supported by wheels passes through the trail to the rear of and below the cradle trunnion support and in front of the point of attachment of the elevating arc. Field guns fell into disuse about 1525 with the introduction of musketry, and remained so until 1631, when Gustavus Adolphus gave artillery its true position on the battlefield.