Considering that the current unit roaster is not reconsidered, what should be the general role of each unit type?
This topic is also discussed on 0 A.D. forums. This page concern the general role, each civilization can have some specificities about some units, but the general role should remain the same not to get lost unnecessary and ease the learning curve.
Spearmen were the core of most armies. Often found heavily armored, or at least with a large shield.
The phalanx was designed for the 2 first row to fight together.
General role: basic infantry, medium melee range
Strength: good armor, good against cavalry (just need to point the incoming target)
Weakness: subject to hit'n run (see Battle of Lechaeum, where Athenians derouted unsupported Spartian hoplites with skirmishers hit'n running them)
Pikemen are a variation of the Greek hoplites with a longer weapon and ligher armor for more mobility and charging abilities.
They compensate their lack of armor with using the pike upward as a deflector for projectiles when in pack.
Also in pack the forest of pikes makes a frontal assault almost a suicide, with multiple rows of soldiers protecting the front (see siege of Atray, were the roman infantry couldn't advance and persian chariots hold in the battle of Gaugamela).
But if very strong from the front, they were almost not able to fight back from the side or back. Once the ennemy has passed the pike, the weapon was almost useless and with no proper armor the pikemen didn't last long (see battle of Pydna, where the Macedonian phallangites were defeated because disorganised by the rough terrain. The Roman took a great advantage once in close quarter).
General role: strong infantry, long melee range
Strength: get the best when in good order and in sufficient number, super strong against cavalry
Weakness: almost ineffective individually or disorganised
Swordsmen are stronger melee infantry. A good sword was expensive and more restricted to an elite.
0 A.D. Design Document
The Roman Testudo allowed them to advance under cover.
General: strong infantry, short melee range
Strength: the best melee fighter one on one
Weakness: short range (less shield effect of 3 on 1), less suited against cavalry
Javelinist are short range support troops. They were usually going before the front infantry line, throw a javelin or two and retreat back to soften the advancing troops. They were also equiped with a secondary melee weapon but not matching their dedicated fellows.
General: infantry support troop, skirmishers
Strength: strong short-range troop, expert of hit'n run (see Battle of Lechaeum), good mobility
Weakness: lightly armored
Slingers were used as skirmishers like javelinists. The finest slingers would use some hi-piercing bullets with great accuracy and long range. A sling shot could be very fast from an experimented slinger.
It was said the slingers could outrange even archers by Xenophon, saying the Ten Thousands couldn't approach the Persian with the lack of slingers or cavalry.
General: infantry support troop, long range mass killers, skirmishers
Strength: longest range troop
Weakness: poorly armored, unprecise (doesn't work well on small targets)
Archers are long range troops. Like their javelinist counterparts they usually acted before the melee battle or target fleeing ennemies. They seemed to be historically efficients with quick long range hi-piercing arrows, and archer continued to exist long after the game period (contrary to some other units).
To distinguish them from javelinists they would be long range support troop unable to hit'n run and very vulnerable to any attack. Still with a shorter range than slingers but better accuracy.
General: long range general purpose unit
Strength: long range
Weakness: poorly armored
The spear cavalry is the heavier one. It is well armored and has the best weapon for pinning down ennemies. Even if it is not the most manœuvrable.
They are so the most expensive cavalry. I haven't found a clear reference cavalry weapons, but they was very often light and heavy cavalry. The spear cavalry would be the heavy one.
Strength: good and reliable cavalry
Weakness: expensive, weak against spears and pikes are their nightmare
Sword was not the weapon of choice to fight mounted. Celtic sword cavalry tend even to fight by foot and get back to their horse afterward.
For the game, they would be the light cavalry. They are best suited for raiding and targeting strategic points (siege units, support troops).
Strength: deal a lot of damage quickly Weakness: not well armored they will not stay long in open fight
Dedicated mounted javelin throwers weren't mentionned historically. They were mostly bound with spear cavalry, throw some javelin as secondary weapon before joining the battle.
For the game, they would be the top hit'n run unit, but more expansive than the infantry javelinists.
Strength: strong at hit'n running, more efficient than their infantry counterpart by being faster
Weakness: because faster than the infantry, they will be lightly armored to be still counterable by other cheaper skirmishers or archers. Otherwise they wouldn't have significant weakness.
Fast long range unit, but rare at that time. Mounted archers will after be the most effective unit in the battlefield, until heavy armored knight came. Historically truely overpowered, combining the strength of the bow with the speed of a horse, even able to shoot back while running away.
Strength: fast and long range, hard to pick
Weakness: poorly armored, to give them a weakness, not so much ability to hit'n run
They were very few elephants in the battles, but they were devastating. Battle tactics often consisted of not fighting the elephants directly.
They were frightened during the battle of Zarma and some of them turned back against the Carthaginian army. The charge was driven past the ranks to be dealt in the back by skirmishers.
Strenght: very durable and powerfull
Weakness: very expansive, can lose control