Thanks IDonT, great links.
Do you know if the crossbowmen exchanged ranks while firing? (what was their routine?)
Any contemporary art of field battles? (I found the picture of the bridge storming btw).
Now back to the original question: what exact time frame are we looking at? Because 200 BC - 200 AD saw a lot of change within the Roman army, from a civilian infantry army to a well balanced army with all types of infantry artillery and cavalry, including a significant amount of very heavily armored knights (Roman or Asian allies / mercenaries).
The former would not venture into open terrain in presence of a cavalry army and the latter had rehearsed methods of how to cope with cavalry masses. That later one would be the most interesting choice.
BeeJay
From the Terracotta army formation. DIfferent dynasty but we can conject that they may fight similarly
Vanguard: 210 unarmoured bowmen and crossbowmen form the vanguard (the front ranks to the east),
standing in 3 rows of 70 warriors. 3 armoured officers stand at both ends and the middle of the first row. The rest of the vanguard is unarmoured, wearing only course tunics girded with belts. Their footwear consisted of puttees and thonged square-toed sandals. The vanguard archers and crossbowmen had a variety of hairstyles but their weapons had deteriorated long ago.
The Main Force: 36 columns of infantrymen and charioteers stand in tight formation behind the vanguard in 9 corridors. All 6,000 warriors in this body wear armour, though the armour varied by functions and ranks. They were supposed to hold spears and halberds in their hands, while wearing bronze swords in wooden scabbards at their waists. However, the wooden parts had since decayed. The 35 4-horse chariots were escorted by infantrymen to offer better protection for the horses.
The Outer Flanks: Occupying the extreme left (northern) and right (southern) corridors are two rows of unarmoured archers in each corridor, facing north and south respectively.
The Rear-guard (to the west) consists of 3 rows, 2 facing front (i.e. east) with the last row facing the rear (i.e. west).
Pit II (the cavalry pit)
It is estimated to contain 80 chariot units and a proportionate (some say equal) number of cavalry, plus about 1,000 support troops consisting of infantry, crossbowmen and archers. The cavalrymen are dismounted, leading their steeds by the bridle (left). Leading this contingent was the figure of a general holding a 2-handed bronze sword.
This force was divided into 5 separate units:
* A vanguard of archers together with unarmoured infantrymen.
* A cavalry unit occupying the left flank.
* A chariot unit occupying the right flank.
* A main unit of cavalry and chariots subdivided into 8 columns occupied t the center in a rectangular formation.
* A cavalry unit covered the rear.
Weapons
Lets keep it in the 200 BC before OCtavius