<P> Fighters travelled in groups of eight, and each octet was sometimes assigned a mule . The mule carried a variety of equipment and supplies, including a mill for grinding grain, a small clay oven for baking bread, cooking pots, spare weapons, waterskins, and tents . A Roman century had a complement of 10 mules, each attended by two non-combatants who handled foraging and water supply . A century might be supported by wagons in the rear, each drawn by six mules, and carrying tools, nails, water barrels, extra food and the tent and possessions of the centurion - commanding officer of the unit . </P> <P> The legion also carried an artillery detachment with 30 pieces of artillery . This consisted of 10 stone - throwing onagers and 20 bolt - shooting ballistas, in addition each of the legion's centuries had its own scorpio bolt thrower (60 total), together with supporting wagons to carry ammunition and spare parts . Bolts were used for targeted fire on human opponents, while stones were used against fortifications or as an area saturation weapon . The catapults were powered by rope and sinew, tightened by ratchet and released, powered by the stored torsion energy . Caesar was to mount these in boats on some operations in Britain, striking fear in the heart of the native opponents according to his writings . His placement of siege engines and bolt throwers in the towers and along the wall of his enclosing fortifications at Alesia were critical to turning back the enormous tide of Gauls . These defensive measures, used in concert with the cavalry charge led by Caesar himself, broke the Gauls and won the battle--and therefore the war--for good . Bolt - throwers like the "scorpion" were mobile and could be deployed in defence of camps, field entrenchments and even in the open field by no more than two or three men . </P> <P> Over time the military system changed its equipment and roles, but throughout the course of Roman history, it always remained a disciplined and professional war machine . Soldiers carried out training common to every organized army, from initial muster, arms and weapons drill, formation marching and tactical exercises . </P> <P> According to Vegetius, during the four - month initial training of a Roman legionary, marching skills were taught before recruits ever handled a weapon; since any formation would be split up by stragglers at the back or soldiers trundling along at differing speeds . Standards varied over time, but normally recruits were first required to complete 20 Roman miles (29.62 km or 18.405 modern miles) with 20.5 kg in five summer hours (the Roman day was divided into 12 hours regardless of season), which was known as "the regular step" or "military pace". They then progressed to the "faster step" or "full pace" and were required to complete 24 Roman miles (35.544 km or 22.086 modern miles) in five summer hours loaded with 20.5 kilograms (45 lb). The typical conditioning regime also included gymnastics and swimming to build physical strength and fitness . </P>

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