Chapter 3 - The Military Revolution
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It was Philip of Macedon who first organized a special group of artillery engineers within his army to design and build catapults. Philip's use of siegecraft allowed Greek science and engineering an opportunity to contribute to the art of war, and by the time of Demetrios I (305 B.C.), known more commonly by his nickname "Poliorcetes" (the Besieger), Greek inventiveness in military engineering was probably the best in the ancient world. Alexander's engineers contributed a number of new ideas. In honor of the Greek contributions, to this day the military art of siege warfare is called "poliorcetics."

The most important contribution of Greek military engineering of this period was the invention of artillery, the earliest of which took the form of catapults and torsion-fired missiles. The earliest examples date from the 4th century B.C. and were called gastraphetes, literally, "belly shooter." It was a form of primitive crossbow that fired a wooden bolt on a flat trajectory along a slot in the aiming rod. Later, weapons fired by torsion bars powered by horsehair and ox tendon (the Greeks called this material neuron ) springs could fire arrows, stones, and pots of burning pitch along a parabolic arc. Some of these machines were quite large and mounted on wheels to improve tactical mobility and deployment. One of these machines, the palintonon, could fire an 8-pound stone over 300 yards, a range greater than that of a Napoleonic cannon. These weapons were all used by Philip as weapons of siege warfare, but it was Alexander who used them in a completely different way -- as covering artillery. Alexander's army carried prefabricated catapults that weighed only 85 pounds. Larger machines were dismantled and carried along in wagons.

Roman advances in the design, mobility, and firepower of artillery produced the largest, longest-ranged, and most rapid-firing artillery pieces of the ancient world. Roman catapults were much larger than the old Greek models and were powered by torsion devices and springs made of sinew kept supple when stored in special canisters of oil. As Josephus recorded in his account of the siege of Jerusalem, the largest of these artillery pieces, the onager, (called the "wild ass" because of its kick), could hurl a 100 pound stone over 400 yards. Vegetius noted that each legion had 10 onagri, one per cohort, organic to its organization. Smaller versions of these machines, such as the scorpion and ballista, were compact enough to be transported by horse or mule. These machines could fire a 7-10 pound stone over 300 yards. Caesar required that each legion carry 30 of these small machines, giving the legion a mobile, organic artillery capability. Smaller machines fired iron-tipped bolts. Designed much like the later crossbow but mounted on small platforms or legs, these machines, which required a two man crew, could be used as rapid-fire field guns against enemy formations. They fired a 26-inch bolt over a range of almost 300 yards. Larger versions mounted on a wheeled frame were called carroballistae and required a 10-man crew. These machines could fire perhaps three to four bolts a minute and they were used to lay down a barrage of fire against enemy troop concentrations. They were the world's first rapid-fire field artillery guns.

The emergence of siegecraft as a basic requirement of Iron Age armies represented a major innovation in warfare. Without the ability rapidly to reduce cities and fortified strong points, no army on the march in hostile territory could hope to force a strategic decision with any rapidity. The very idea of empire would have been militarily unthinkable in much the same way as it was for the classical Greek armies which had no siegecraft capability. The search for more efficient ways to destroy fortifications produced, perhaps somewhat by accident, the new combat arm of artillery. While Alexander was the first to use it, the Romans gave birth to the idea of using artillery as antipersonnel weapons. Both siege engines and artillery represent the birth of a major new idea in the technology of war, an idea that came to further fruition with introduction of gunpowder a thousand years later.

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