Despite the rise of, knightly cavalry in the 11th century, infantry played an important role throughout the Middle Ages on both the battlefield and in sieges. From the 14th century onwards, it has been argued that there was a rise in the prominence of infantry forces, sometimes referred to as an "infantry revolution", but this view is strongly contested by some military historians.

Cost, recruitment, and growth

Rising costs of war In the medieval period, the mounted warrior held sway for an extended time. Typically heavily armoured, well-motivated and mounted on powerful, specially bred horses, the mounted knight represented a formidable force, which was used to effect against more lightly armoured troops. Since only the noble classes could afford the expense of knightly warfare, the supremacy of the mounted cavalryman was associated with the hierarchical structure of medieval times, particularly feudalism. As the period progressed, however, the dominance of the cavalry elite began to slowly break down. The Black Death in the 14th century swept through Europe, devastating the population and resulting in serious manpower shortages. This encouraged more economical use of available manpower, and the infantryman was much cheaper to outfit and maintain than the aristocratic knight. The Crusade era highlighted the importance of infantry and required large numbers of men and material to be organized for distant battlefields, but foot was consistently a central element in medieval armies. Such expeditions were part of the growing number of sieges, disputes and campaigns throughout the 13th and 14th centuries that greatly increased the cost of warfare for medieval regimes. The relative inexpensiveness of the infantryman, combined with a shortage of manpower, provided incentives for expanding their use.

Recruitment By the 11th century, much of the infantry fighting was conducted by high-ranking nobles, middle-class freemen and peasants, who were expected to have a certain standard of equipment, often including helmet, spear, shield and secondary weapons in the form of an axe, long knife or sword. Peasants were also used for the role of archers and skirmishers, providing missile cover for the heavy infantry and cavalry. The High Medieval period also saw the expansion of mercenary forces, unbound to any medieval lord. Routiers, such as Brabançons and Aragones, were supplemented in the later Middle Ages by Swiss pikeman, the German Landsknecht, and the Italian Condottiere - to provide the three best-known examples of these bands of fighting men. It has been argued that the expanded campaigns, castle-building and sieges of the era also saw greater use of household troops, often bodyguards of the elite, with a variety of useful skills. These were cheaper to recruit and maintain than knights with all their trappings, such as the renowned crossbowmen in Richard I's crusading mesnée in the late 12th century. Siege warfare, in particular, required large bodies of troops in the field, for extended periods, including numerous specialists. All this added up to make the early days of peasant levies unsustainable. As more kings and lords turned to infantry, their opponents had to keep pace, leading to additional increases in foot troops. To obtain the best fighting men, elites had to make provision for their regular payment and supply. As Clifford Rogers, historian of medieval warfare notes:

Organisation and deployment

Organisation The importance of good order was well understood in medieval warfare: Militia forces were often organised by guilds or districts, with their officers and banners. Swiss muster rolls show officers and standard bearers being appointed, and men being assigned to particular positions in the formation.Miller (1979), pp17, 24 Various accounts show that it was the role of commanders to make sure their men knew their position in the formation, knew which banners they fought under and who stood around them.

Formations Philippe Contamine identifies three basic infantry formations in the Middle Ages; the wall, the circle or crescent and the deep solid formation, either rectangular or triangular.

Shieldwall Linear formations existed throughout the medieval period. In the early Middle Ages, infantry used the Shieldwall, a formation where shields were held edge-to-edge or overlapped, but lines persisted beyond the widespread abandonment of shields in the later Middle Ages. Lines could vary in depth from four to sixteen deep and were drawn up tightly packed.

All round defence This formation, called the crown by J. F. Verbruggen, was used by infantry to form an all round defence against cavalry. It is recorded as having been used by Flemings, Swiss, Scots and Scandinavians.

Deep formations Deep columns were favoured by the Swiss. A reconstruction of the deployment of Zürich forces in 1443 gives a formation 56 men wide by 20 deep, the formation having a width of and a depth of . The Swiss main formation at the Battle of Morat consisted of 10,000 men, the outer four ranks being made up of pikemen, the inner ranks of halberdiers, the force having an estimated area of .

Triangular formations were also used, this sometimes being described as "in the manner of a shield" (). Wedge formations were used by the Vikings under the name of a "swine wedge" ().Griffiths(1995), p.189 The Swiss also sometimes used a keil or wedge of pikes to lead their columns.

Against other types of combatants

Against cavalry Tactically there were only two ways for infantry to beat cavalry in an open field battle: firepower and mass. Firepower could be provided by swarms of missiles. Mass could be provided by a tightly packed phalanx of men.James M. Powell, Anatomy of a Crusade: 1213-1221, University of Pennsylvania Press, 1986 Such tactics were long-established; the Romans used missile troops such as slingers, and the core infantry learned to deal with swarming enemy cavalrymen by forming a hollow square fenced with a solid hedge of iron pila (large javelins). Alexander the Great combined both methods in his clashes with the Asiatic horseman of Persia and India, screening his central infantry phalanx with slingers, archers and javelin-men, before unleashing his cavalry against the enemy. Both mass and firepower could be aided by a good tactical position, such as on a hill or on rough terrain, where enemy cavalry would have trouble manoeuvring. These ancient lessons were relearned in the medieval period: in the Crusades, in the continued operations of forces like the Flemish footman, and particularly the Swiss pikeman and the English longbowman.

The Crusades offer an illustration of the growing recognition of the need for infantry. Against the mounted Islamic foes of European armies, infantry forces were of vital importance. Archers, for example, were essential in holding the fast-moving Muslim cavalry at bay—suppressing their firepower, and allowing the armoured knights to mount successful counter-attacks. Pikemen were important in screening the flanks of the Christian forces, always vulnerable to assault by the Turkish horsemen. Against Saladin's light cavalry at Jaffa (c. 1192) during the Crusades, Richard of England drew up a line of spearmen, kneeling on the ground with spear planted in front, forming an effectual 'hedge of steel' against the charging enemy horsemen. Behind the spear wall, crossbowmen stood ready, with assistants helping to reload. The Muslim armies attacked but the combined firepower of the archers and the steadiness of the wall of spears held. Once the Muslims pulled back, Richard ordered his armoured knights forward, and Saladin withdrew. At the battle of Courtrai in 1302, the determined Flemish infantry staked out a good position on advantageous ground (cut up with streams and ditches) and stood firm against the cavalry charge of the French nobles using their pikes and wooden Goedendag, a combination spear and club. The French charge was stopped and the Flemish infantry then moved forward to liquidate the opposition. At Bannockburn, the Scottish fighters dug numerous pits to foil the English cavalry, blunted the English advance, then counter-attacked with their pike army to soundly defeat their opponents. These and other examples illustrate the importance of trained infantry, but the dominance of the footman did not come overnight. Both cavalryman and infantryman continued to operate for long periods side by side throughout the medieval period.

Against other infantry The essential elements of success in infantry combat were seen as good order and a tight formation, not impetus. During the Hundred Years' War, it was considered disadvantageous for infantry to be forced to attack. If infantry were forced to advance to the attack, it should be at a slow, steady pace and without turning. The actual mechanics of impact are not, however, fully understood. In his reconstruction of the infantry fight at Agincourt, John Keegan describes the French as running to contact over the final yards but the English stepping back to "wrong foot" them. The English gave back a "spear's length", leaving the two bodies spear fencing at a distance of 10–15 ft. This idea of a space between the battlelines in which combat takes place also features in some reconstructions of shield wall combat. Others see the clash of shield walls as involving the physical impact of one line with the other.Pollington(1996), p.184

While it was known for a poorly arrayed line to disintegrate on contact with the enemy, it was more usual for a static battle to ensue and last for some time. Combat was not constant, the two sides parting to rest and reorganise. This could happen several times during combat. When it wasn't possible, an infantry force could become compressed and disordered with disastrous consequences, as happened at Agincourt and Westrozebeke.

Role of archery The traditional role of archery on the medieval battlefield was to begin the action, advancing in front of the main body of the army, as occurred at the Battle of Hastings. This continued to be a standard tactic, particularly in the absence of enemy cavalry. The Swiss crossbowmen and handgunners of the 15th century were notable for their aggressive skirmishing in advance of the main army, as at Morat. To protect archers, particularly crossbowmen, against enemy archers, they were often deployed behind men with large shields, called pavises. This technique is first noted during the Crusades in the 12th century, for example at Jaffa, but was particularly common in Italy in the later Middle Ages. The crossbow began to replace the standard bow throughout Europe in the 12th century. In England and Wales, the longbow and in the Iberian Peninsula (Portugal and Spain) the recurved bow continued in use to the end of the period. Christian Spain owed the use of composite bows and mounted archery using Parthian shots to its long exposure to Islamic military techniques during the Reconquista.

Later in the Middle Ages, massed archery techniques were developed. English and Welsh longbowmen in particular were famed for the volume and accuracy of their shooting, to which cavalry and poorly armoured infantry were particularly vulnerable.

In siege