As a tactician Hannibal excelled, and his tactics were more flexible than those of Alexander because the organization of his army was far more fluid. He was a master of stratagem and sur prise, but in siege craft he fell a long way behind the great Mace donian, otherwise Rome would have been his. At the battle of the Trebia (q.v.) in 218 B.C. he made full use of fire power to dis organize the Roman attack. Sempronius pushed back his centre, exposed his own wings to envelopment, and was charged by Mago in rear. At Lake Trasimenus in the following year Flaminius was surprised in a defile, he was deprived of front, rear and flanks, and his army was destroyed. The tactics Hannibal em ployed at the battle of Cannae (q.v.) in 216 B.C. have never ceased to be quoted; they were an improvement on those used at the Trebia, were somewhat similar to those of Miltiades at Marathon, and of Hindenburg at Tannenberg (q.v.) in 1914. Hannibal's grand tactical idea was that of the active defence. In place of forming a stable centre, as Alexander did, he formed a flexible one thrown forward in a half moon formation so that when it was pushed back it would gain rigidity. Had it been a line, as was the case at Marathon, when forced to retire it might well have been broken. On the flanks of this central arch Hannibal hinged two flexible cavalry wings. The Romans forced back this living arch into a line, into a pocket, then Hasdrubal in command of the right cavalry wing wheeled round their left flank and charged them in rear. Their defeat was absolute. By 207 B.C. the Romans had learnt their lesson, and at the Metaurus (q.v.) it was Nero's attack on the rear of Has drubal's right flank which won him the day. Five years later at Zama Laelius and Massinissa fell on the rear of Hannibal's line and his defeat was total.
Marius and Caesar.—After Zama the golden age of Roman tactics pales. There are many great battles, but mostly against ill-equipped barbarians. Technical rather than tactical perfection grows apace, and from an art war sinks into a trade. By the re forms of Marius (107 p.c.) the 3o maniples of the legion were converted into io cohorts, in all about 6,000 men. The distinction between velites, hastati, principes and triarii were abolished; the legionaries were all armed alike with a heavy javelin (pi/um) and the short Spanish sword (gladius) ; the cavalry were removed from its organization, and the 3-line formation was replaced by a 2-line one, each of 5 cohorts at close distance. The veterans being in the first line. Such was the legion under Caesar, a cautious hard-headed tactician, a great administrator and a born diploma tist whose main contribution to tactics was his use of reserves. He solved the problem of how to sustain a frontal attack and simultaneously repulse an attack on flanks or rear. In his Af rican war, on the open plain near Ruspina (46 B.c.), he was en veloped by the Numidian horse. Forming his troops into one line
he ordered alternate cohorts to face about, burst through the Numidian ring with his flanking cohorts, and then charged the fragments. A similar manoeuvre was devised by Bouquet, about 1760, in his war with the red Indians in America. Caesar made great use of entrenched camps, converting them into movable fortresses to aid in victory, and to provide a rallying point in the event of defeat. As a strategist he fully grasped the value of an attack on his enemy's communications, and as a tactician he aimed at surprise, maintained an excellent system of scouting, but with the exception of his tactics at Ruspina he introduced no new for mation of attack.
The Army of the Empire.—Under Augustus the changes which were taking form in the legion during the Civil Wars were brought to a head. The army of the republic was a burgess militia ; this had been largely replaced by professional soldiers and mercenaries. From this somewhat heterogeneous body of men Augustus created a standing army of 25 legions with cavalry at tached. These were mainly quartered in permanent camps on the Rhine, Danube and Euphrates, and to them were frequently added large numbers of barbarian auxiliaries. For the protection of Italy Augustus raised ten praetorian cohorts of ',coo men each. The total strength of the army under the early empire has been estimated at 300,00o men.
The main tendency of tactics now became defensive, the army by degrees approximating to a police force with two main duties, namely, internal security and frontier defence. The sword was largely discarded in preference for the spear, and so many missile weapons were added that hand-to-hand conflicts became the ex ception rather than the rule. The same forces were at work which modified the Hellenistic armies after the death of Alexander. Increase in wealth was followed by improvement in engineering and fortifications, with the result that artillery, both light and heavy, became the preponderating arm. At the siege of Massilia Caesar's soldiers had to protect themselves against projectiles with mantlets a foot thick. In A.D. 69, in a battle fought near Cre mona between Vitellius and Vespasian, Tacitus tells us that the 15th Legion possessed a huge balista which would have de stroyed the enemy's line had it not been damaged by two soldiers who risked their lives in the destruction of its mechanism. By the 4th century, according to Vegetius, each cohort was equipped with one catapult, and each century with one carro-balista which required z I men to work it. Consequently the legion possessed an artillery train of ten "guns" and 6o "howitzers," that is ap proximately ten pieces to each z,000 infantry, an exceedingly high proportion seeing that in Napoleon's time the number was gen erally three to I,000, and even to-day it is seldom more than four or five to I,000.