The infantry are the guys that most people imagine when they hear the word soldier. In most cases they are of the same opinion themselves.
An infantryman's equipment may change, but the job is more or less the same throughout history - and is unlikely to change much in the future. These are the men who will be expected to do most of the fighting - to fix, engage and destroy the enemy and to occupy and defend objectives against counter-attack. Cavalry may be able to take ground - sometimes - but only infantry can hold it.
As previously implied, the job is old - as old as civilisation infact - and the status and equipment of the infantry has varied from place to place, depending on the culture and their preferred means of making war. In many places the cavalry were the social and military elite and the infantry composed of people that couldn't afford a horse … in others, the infantry were the main feature and the cavalry a sideshow. Regardless, there are two main classifications of infantry heavy infantry and light infantry - and it is important to recognise that it is role, not equipment, that divides the two.
Heavy infantry are meant to fight in close order and engage the enemy directly - historically these were the men who moved about the battlefield in solid masses, collided with one another and decided the course of things by melee. As the name implies they were often - but not always - equipped with heavy armour, large shields and melee weapons. Missile equipped heavy infantry were rare but not unknown - for example many English Longbowmen fought in this role. Further examples might be the post-Marian Roman Legionary (mail armour, large shield, stabbing sword and javelin), Persian Immortal (scale armour, spear, large shield, bow and slashing sword) and the Hellenistic Phalangist (unarmoured or linothorax armoured, small shield, pike and slashing sword). Equally, medieval levies crammed together in an improvised shield wall also count as heavy infantry, as do the armies of mass of the early modern period.
In the modern era, the heavy role is fulfilled by armoured infantry, mounted in infantry fighting vehicles and operating in close mutual support with tanks. Ironically, these men may actually carry less equipment than their colleagues in the light infantry.
The light infantry is where the designation by role becomes really significant. The light infantry's job is usually to do with skirmishing and patrolling and centres around winning the reconaissance battle and taking control of no-man's land to deny the enemy the ability to manouver and deploy freely. They are also typically expected to move and fight in rough terrain where the close order formations of heavy infantry would be ineffective. What this means for men and equipment is anyone's guess. In some eras, light infantry were made up of those too poor to afford the equipment to fight as heavy infantry and were more or less deployed as a cloud of flies around the formations of better equipped men - much of the classical Greek era and the pre-Marian Romans tended towards this. Ideally such men carried ranged weapons and could direct harrassing fire onto enemy formations even if - as in the case of Roman leves or Greek gymnatokoi - this consisted merely of flinging stones at them. Properly deployed, light infantry skirmishers could be a battle winner (as when Athenian peltasts sucessfully demolished a Spartan regiment at Lechaeum when it took the field without its own skimisher support), but generally their role was limited to weakening and disrupting enemy heavy units and/or goading them into charges or into rough ground. For much of history, the light role was the default for missile armed troops. However, light troops were not always low status or lightly equipped - a prime example being the "Peltasts" deployed by some of the Hellenistic states. Traditionally a peltast was a light infantryman, protected only by a small shield (known as a pelta) and equipped with javelins and a sword or dagger. Some of the late Hellenic peltasts, by contrast were elite assault troops - still fighting in open order (hence the light designation) but heavily armoured and specialising in sword combat, often used to lead storming parties against fortified positions.
In the modern era, light units are very often elite formations, trained for special roles such as mountain, amphibious or airborne wafare - they continue the light infantry tradition of controlling parts of the battlefield in which heavy units are not deployed and/or unable to manouver and typically are equipped on lighter scales than heavy units (for example, if they are issued vehicles at all, they will tend to be soft-skins rather than armoured fighting vehicles). Light troops may also deploy by watercraft or from aircraft. The US (and some other powers) have a confusing habit of referring to some motorised or helicopterborne infantry as cavalry1. Of course, in many modern nations, the same infantry units can fight as heavy or light troops and will, ironically, be classified depending on the equipment they deploy with.
A third, contentions class is that of medium infantry. This is more of a theoretical designation and some authorities discard it altogether, but in general it can be applied to historical units that fought as both light and heavy infantry depending on need. The classical greek ekdromoi2 are a good, early example - men with standard hoplite equipment (but unarmoured), selected for running ability, whose job was to sprint out from the phalanx and engage enemy skimishers as required and otherwise to fight as ordinary hoplites in the phalanx. Roman Antesigni fulfilled much the same role. Medium units were often used as flankers to heavy troops - another example being the Hellenistic theurophoroi who where deployed on the flanks of the phalanx and, being equipped with spear, sword, javelins, light armour and the large "theuros" shield, could fight as either a close order extension of the phalanx, or light role skirmishers as required. Theurophoroi are also recorded as being used to clear and capture close terrain in which the phalanx would struggle, using their open order and heavier equipment to overwhelm lighter skimishers. Many primitive troops can be seen as fighting as medium troops by default - manouvering in a block to some degree, but with a tendency to break the battle down into a series of private melees once the engagement begins.
In the modern era … well, as noted above, some authorities would say that most troops (at least in the developed world) are medium now. Others would apply the term to troops fighting in a heavy role but without a full scale of equipment and/or without attached tank units. For much of the cold war period, both sides maintained formations of mechanised infantry mounted in armoured personnel carriers, without the organic tanks of an armoured formation but intended to operate in support of armoured units. These "mechanised infantry3" might also be considered medium, as might any other infantry deployed as heavy units but not thus equipped.
Independant of "weight" there is also the concept of mounted infantry. Although these men are sometimes mistaken for cavalry, the key difference is that they do not fight from the saddle, but instead use their mounts for increased mobility whilst disengaged. This confusion is not helped at all by the ability of most cavalry to fight dismounted, but as a rule of thumb, if it can fight mounted, it's a cavalry unit. For most of history mounted infantry used horses or mules as transport, but in the early modern period there was a significant use of bicycle infantry as well. As previously noted, modern infantry tend to be far more extensively "mounted".
Game and Story Use
- Infantry work can be tricky to make a campaign out of - light units are probably best as they are mostly likely to be assigned special duties in most eras (unless, as in the Roman case, they're just the hired help). Your best bet is probably to use the regiment as a depot, from which the PCs are sent out on special duties. Medium units might be even better if you hold with such things - who better to conduct some special operation on behalf of the polis than the ekdromoi? If the strategos needs some reliable citizens (as opposed to the ephebes, freedmen and metics serving in the skirmish line) to detach for a special job, there they are. Recycle as required for other cultures.
- For most of history, this is (statistically at least) the arm in which most soldiers served - with a few exceptions for armies like the Huns or the Mongols. Only from the late twentieth century have rear-echelon troops started to outnumber front line ones.
- Expect more pathos in an infantry story - the cavalry gallop about having adventures, the infantry are more likely to get accquainted with mud and close combat. If there are shortages of anything, the infantry will be the first to notice.
- Iron rations are usually a key feature of the infantryman's life.