Roman infantry tactics

Roman infantry tactics are the theoretical and historical deployment, formation, and manoeuvres of the Roman infantry from the start of the Roman Republic to the fall of the Western Roman Empire. The focus below is primarily on Roman tactics: the "how" of their approach to battle, and how it stacked up against a variety of opponents over time. It does not attempt detailed coverage of things like army structure or equipment. Various battles are summarized to illustrate Roman methods with links to detailed articles on individual encounters.

The original Roman army was made up of hoplites, whose main strategy was forming into a phalanx. By the early third century BCE, the Roman army would switch to the maniple system, which would divide the Roman army into three units, hastati, principes, and triarii. Later, in 107 BCE, Marius would institute the so-called Marian reforms, creating the Roman legions. This system would evolve into the Late Roman Army, which utilized the comitatenses and limitanei units to defend the Empire.

Roman legionaries had armour, a gladius, a shield, two pila, and food rations. They carried around tools such as a dolabra, a wooden stave, and a shallow wicker basket. These tools would be used for building castra (camps). Sometimes Roman soldiers would have mules that carried equipment. Legionaries carried onagers, ballistae, and scorpios.

Roman soldiers would train for four months. They learned marching skills first, followed by learning how to use their weapons. Then they began to spar with other soldiers. During the training exercise, the soldiers would also be taught to obey their commanders and either the Republic or the Emperor.

Legions were divided into units called cohorts. Each cohort was divided into three maniples. Each maniple was divided into centuries. Several legions made up field armies.

During the Republic consuls, proconsuls, praetors, propraetors, and dictators were the only officials that could command an army. A legatus assisted the magistrate in commanding the legion. Tribunes oversaw the logistics of the army. Centurions commanded the centuries (groups of about 100 soldiers). The Roman army would be supplied by purchasing agents that would buy provisions. Local peasants or farmers might have their supplies taken from them in order to supply the Roman legion. Roman soldiers would build infrastructure such as roads or supply caches while on the march. Some equipment was moved by pack animals and carts. Traders, hucksters, prostitutes, and other miscellaneous service providers would also follow the marching legion.

While marching, the legion would deploy in several columns with a vanguard before them. This formation would be surrounded by soldiers on the flanks. Afterwards, the soldiers would construct a fortified camp. After staying in the camp for some time, the army would destroy the camp to prevent its use by the enemy, and then continue moving. The commanders of the Roman army might try to gather intelligence on the enemy. During the march, the commander would try to boost the morale of his soldiers.

Before a battle, the commander would try to manoeuvre his army in a way that granted him the advantage. If the battle was fought when the maniple system was in place, the army would have the hastati in the front, the principes in the middle, and the triarii in the back. Skirmishers called velites would be placed in front of the army in order to throw javelins at the enemy. Once the so-called Marian reforms were enacted, the same formations and strategies continued to be used. However, instead of hastati, principes, and triarii they used cohorts.

When conducting a siege the army would begin by building a military camp. Then they would use siege weapons and the soldiers to assault the city and take it. When defending a city they built palisades, assault roads, moles, breakwaters, and double walls. The legions also would build a camp.