Heavy infantry in the context of Firearm

The phalanx (pl.: phalanxes or phalanges) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar polearms tightly packed together. The term is used today to describe the use of this formation in ancient Greek warfare, but ancient Greek writers used it more broadly to describe any massed infantry formation regardless of its equipment. In Greek texts, the phalanx may be deployed for battle, on the march, or even camped, thus describing the mass of infantry or cavalry that would deploy in line during battle. They marched forward as one entity.

The term itself, as used today, does not refer to a distinctive military unit or division (e.g., the Roman legion or the contemporary Western-type battalion), but to the type of formation of an army's troops. Therefore, this term does not indicate a standard combat strength or composition but includes the total number of infantry, which is deployed in a single formation known as a "phalanx".

Infantry, or infantryman are a type of soldier who specialize in ground combat, typically fighting dismounted. Historically the term was used to describe foot soldiers, i.e. those who march and fight on foot. In modern usage, the term broadly encompasses a wide variety of subspecialties, including light infantry, irregular infantry, heavy infantry, mountain infantry, motorized infantry, mechanized infantry, airborne infantry, air assault infantry, and naval infantry. Other subtypes of infantry, such as line infantry and mounted infantry, were once commonplace but fell out of favor in the 19th century with the invention of more accurate and powerful weapons.

Light infantry refers to certain types of lightly equipped infantry throughout history. They have a more mobile or fluid function than other types of infantry, such as heavy infantry or line infantry. Historically, light infantry often fought as scouts, raiders, and skirmishers. These are loose formations that fight ahead of the main army to harass, delay, disrupt supply lines, engage the enemy's own skirmishing forces, and generally "soften up" an enemy before the main battle. Light infantrymen were also often responsible for screening the main body of a military formation.

Following World War II, the term "light infantry" has evolved to include rapid-deployment units (including commando and airborne units) that emphasize speed and mobility over armor and firepower. Some units or battalions that historically held a skirmishing role retain their designation "light infantry" for the sake of tradition.

The spatha was a type of straight and long sword, measuring between 0.5 and 1 metre (20 and 40 inches), with a handle length of between 18 and 20 centimetres (7 and 8 inches), in use in the territory of the Roman Empire during the 1st to 6th centuries AD. Later swords, from the 7th to 10th centuries, like the Viking swords, are recognizable derivatives and sometimes subsumed under the term spatha.

The Roman spatha was used in war and in gladiatorial fights. The spatha of literature appears in the Roman Empire in the 1st century AD as a weapon used by presumably Celtic auxiliaries and gradually became a standard heavy infantry weapon by the 3rd century AD, relegating the gladius to use as a light infantry weapon. The spatha apparently replaced the gladius in the front ranks, giving the infantry more reach when thrusting. While the infantry version had a long point, versions carried by the cavalry had a rounded tip that prevented accidental stabbing of the cavalryman's own foot or horse.

The Byzantine army was the primary military body of the Byzantine armed forces, serving alongside the Byzantine navy. A direct continuation of the Eastern Roman army, shaping and developing itself on the legacy of the late Hellenistic armies, it maintained a similar level of discipline, strategic prowess and organization. It was among the most effective armies of western Eurasia for much of the Middle Ages. Over time the cavalry arm became more prominent in the Byzantine army as the legion system disappeared in the early 7th century. Later reforms reflected some Germanic and Asian influences—rival forces frequently became sources of mercenary units, such as the Huns, Cumans, Alans and (following the Battle of Manzikert) Turks, meeting the Empire's demand for light cavalry mercenaries. Since much of the Byzantine military focused on the strategy and skill of generals utilizing militia troops, heavy infantry were recruited from Frankish and later Varangian mercenaries.

From the 6th to the 12th centuries, the Byzantine army was among the most powerful and effective military forces in the world – neither Middle Ages Europe nor (following its early successes) the fracturing Caliphate could match the strategies and the efficiency of the Byzantine army. Restricted to a largely defensive role in the 7th to mid-9th centuries, the Byzantines developed the theme system to counter the more powerful Caliphate. From the mid-9th century, however, they gradually went on the offensive, culminating in the great conquests of the 10th century under a series of soldier-emperors such as Nikephoros II Phokas, John Tzimiskes and Basil II. The army they led was less reliant on the militia of the themes; it was by now a largely professional force, with a strong and well-drilled infantry at its core and augmented by a revived heavy cavalry arm. With one of the most powerful economies in the world at the time, the Empire had the resources to put to the field a powerful host when needed, in order to reclaim its long-lost territories.

The Battle of Cannae (/ˈkæni, -eɪ, -aɪ/; Latin: [ˈkanːae̯]) was a key engagement of the Second Punic War between the Roman Republic and Carthage, fought on 2 August 216 BC near the ancient village of Cannae in Apulia, southeast Italy. The Carthaginians and their allies, led by Hannibal, surrounded and practically annihilated a larger Roman and Italian army under the consuls Lucius Aemilius Paullus and Gaius Terentius Varro. It is regarded as one of the greatest tactical feats in military history and one of the worst defeats in Roman history, and it cemented Hannibal's reputation as one of antiquity's greatest tacticians.

Having recovered from their losses at Trebia (218 BC) and Lake Trasimene (217 BC), the Romans decided to engage Hannibal at Cannae, with approximately 86,000 Roman and allied socii troops. They massed their heavy infantry in a deeper formation than usual, while Hannibal used the double envelopment tactic and surrounded his enemy, trapping the majority of the Roman army, who were then slaughtered. Later historians and military strategists have used Cannae as an exemplary battle of annihilation. The loss of life on the Roman side meant it was one of the most lethal single days of fighting in history; historian Adrian Goldsworthy equates the death toll at Cannae to "the massed slaughter of the British Army on the first day of the Somme offensive in 1916". Only about 15,000 Romans, most of whom were from the garrisons of the camps and had not taken part in the battle, survived. Following the defeat, Capua and several other Italian city-states defected from the Roman Republic to Carthage.

The Battle of Carrhae (Latin pronunciation: [ˈkar.rʰae̯]) was fought in 53 BC between the Roman Republic and the Parthian Empire near the ancient town of Carrhae (present-day Harran, Turkey). An invading force of seven legions of Roman heavy infantry under Marcus Licinius Crassus was lured into the desert and decisively defeated by a mixed cavalry army of heavy cataphracts and light horse archers led by the Parthian general Surena. On such flat terrain, the legion proved to have no viable tactics against the highly mobile Parthian horsemen, and the slow and vulnerable Roman formations were surrounded, exhausted by constant attacks, and eventually crushed. Crassus was killed along with most of his army. It is commonly seen as one of the earliest and most important battles between the Roman and Parthian Empires and one of the most crushing defeats in Roman history. According to the poet Ovid in Book 6 of his poem Fasti, the battle occurred on 9 June.

Crassus, a member of the First Triumvirate and the wealthiest man in Rome, had been enticed by the prospect of military glory and riches and decided to invade Parthia without the official consent of the Senate. Rejecting an offer from the Armenian King Artavasdes II to allow Crassus to invade Parthia via Armenia, Crassus marched his army directly through the deserts of Mesopotamia. His forces clashed with Surena's troops near Carrhae. Surena's cavalry killed or captured most of the Roman soldiers. Crassus himself was killed when truce negotiations turned violent, and his death ended the First Triumvirate.

Skirmishers are light infantry or light cavalry soldiers deployed as a vanguard, flank guard or rearguard to screen a tactical position or a larger body of friendly troops from enemy advances. They may be deployed in a skirmish line, an irregular open formation that is much more spread out in depth and in breadth than a traditional line formation. Their purpose is to harass the enemy by engaging them in only light or sporadic combat to delay their movement, disrupt their attack, or weaken their morale. Such tactics are collectively called skirmishing. An engagement with only light, relatively indecisive combat is sometimes called a skirmish even if heavier troops are sometimes involved.

Skirmishers can be either regular army units that are temporarily detached to perform skirmishing or specialty units that were specifically armed and trained for such low-level irregular warfare tactics. Light infantry, light cavalry (historically), and irregular units often specialize in skirmishing. Skirmishers' open formations and smaller numbers can give them superior mobility over the regular forces, allowing them to engage only on favorable terms, taking advantage of better position or terrain, and quickly withdrawing from any threat of superior enemy forces. Though often critical in protecting the main army from sudden enemy advances, skirmishers were historically poor at taking or defending ground from heavy infantry or heavy cavalry.

A Spartiate (Greek: Σπαρτιάτης, Spartiátēs) or Homoios (pl. Homoioi, Greek: Ὅμοιος, "alike") was an elite full-citizen man of the ancient Greek city-state of Sparta. They served as one of the city-state's ruling bodies, as well as heavy infantry in times of war. Known for their militaristic indoctrination since childhood, the Spartiate became renowned for their prowess in battle. However, their population decreased overtime due to strict qualification, which affected the city-state in the years to come.

The Marian reforms were putative changes to the composition and operation of the Roman army during the late Roman Republic usually attributed to Gaius Marius (a general who was consul in 107, 104–100, and 86 BC). The most important of these concerned the altering of the socio-economic background of the soldiery. Other changes were supposed to have included the introduction of the cohort; the institution of a single form of heavy infantry with uniform equipment; the universal adoption of the eagle standard; and the abolition of the citizen cavalry. It was commonly believed that Marius changed the soldiers' socio-economic background by allowing citizens without property to join the Roman army, a process called "proletarianisation". This was thought to have created a semi-professional class of soldiers motivated by land grants; these soldiers in turn became clients of their generals, who then used them to overthrow the republic.

Belief in a comprehensive scheme of reforms under Marius emerged in 1840s German scholarship, which posited that any changes in the Roman army between the times of Polybius and Marius were attributable to a single reform event. This belief was spread relatively uncritically and was accepted as largely proven by the 1850s and through much of the 20th century. There is, however, little ancient evidence for any permanent or significant change to recruitment practice in Marius' time. The occurrence of such a comprehensive reform led by Marius is no longer widely accepted by specialists; 21st-century scholars have called the reforms a "construct of modern scholarship".

A pitched battle or set-piece battle is a battle in which opposing forces each anticipate the setting of the battle, and each chooses to commit to it. Either side may have the option to disengage before the battle starts or shortly thereafter. A pitched battle is not a chance encounter such as a meeting engagement, or where one side is forced to fight at a time not of its choosing such as happens in a siege or an ambush. Pitched battles are usually carefully planned to maximize one's strengths against an opponent's weaknesses and use a full range of deceptions, feints, and other manoeuvres. They are also planned to take advantage of terrain favourable to one's force. Forces strong in cavalry, for example, will not select swamp, forest, or mountain terrain for the planned struggle. For example, Carthaginian General Hannibal selected relatively flat ground near the village of Cannae for his great confrontation with the Romans, not the rocky terrain of the high Apennines. Likewise, Zulu Commander Shaka avoided forested areas or swamps, in favour of rolling grassland (flat or on mountain slopes), where the encircling horns of the Zulu Impi could manoeuvre to effect. A pitched battle can decide the outcome of a war or military operation. Pitched battles continued to evolve throughout history as armies implemented new technology and tactics.

During the Prehistorical period, pitched battles were established as the primary method for organised conflict and placed an emphasis on the implementation of rudimentary hand and missile weapons in loose formations. This developed into the Classical period as weapons and armour became more sophisticated and increased the efficacy of heavy infantry. Pitched battles decreased in size and frequency during the Middle Ages and saw the implementation of heavy cavalry and new counter cavalry formations. The early modern period saw the introduction of rudimentary firearms and artillery developing new tactics to respond to the rapidly changing state of gunpowder warfare. The late modern period saw improvements to firearms technology which saw the standardisation of rifle infantry, cavalry and artillery during battles. Pitched battles declined towards the late 19th century and had ceased by the First World War because of technological developments establishing trench warfare. Whilst there are a few examples of pitched battles that occurred on a large scale during the Second World War, during the Post-war period, pitched battles effectively ceased to exist because of the prevalence of irregular warfare. The largest set-piece battle in the history of warfare was the Battle of Kursk.

The army of Carthage (Punic: 𐤓𐤌 𐤐𐤕 𐤒𐤓𐤕𐤂𐤍) was one of the largest military forces in the ancient world. Although Carthage's navy was always its main military force, the army acquired a key role in the spread of Carthaginian power over the native peoples of northern Africa and southern Iberian Peninsula from the 6th century BC and the 3rd century BC. Carthage's military also allowed it to expand into Sardinia and the Balearic Islands. This expansion transformed the military from a body of citizen-soldiers into a multinational force composed of a combination of allies, citizens and foreign mercenary units.

The Carthaginian military was a combined arms force, which comprised light and heavy infantry, siege engines, skirmishers, light and heavy cavalry, as well as war elephants and chariots. Supreme command of the military was initially held by the civilian Suffetes until the third century BC. Thereafter, professional military generals were appointed directly by the Carthaginian Senate.