Monday 16 October 2023

Battle of Idistaviso 16AD using When Warriors Collide


This is game 64 in play testing my ancient rules by replaying historical battles.  I am using another set of my rules When Warriors Collide (WWC).  I am in the process of writing up the rules but the current draft is here.  I am play testing rules by replaying all the Peter Sides scenarios from his Historical Battles books.  WWC is designed to finish in around 30 minutes on a 2’x2’ or smaller table; I am currently using a 40cmx40cm table.

Battle of Idistaviso 16AD

This battle was between the Roman force led by Germanicus, and various German tribes commanded by Arminius. This marked the end of Germanicus’s 3 year campaign in Germania.


TMP discussion:





4 HI Legions

2 MI Auxilia

2 LI Auxilia

2 HC Heavy Cavalry


Breakpoint: 4



6 WB Warbands

2 LI Light infantry

1 HC Cavalry


Breakpoint: 4


Note: Breakpoints are now simply ½ non-light units.

 Scenario changes

Reduced force sizes to fit on the small table.


Deployment.  Romans at the top, Germans at the bottom. 


The complete Roman line advances, as does the Germans.

The lines are close

The German left flank cavalry charges the Roman light infantry that attempt to fire but rout instead.  The German cavalry pursues into the Roman Auxilia and in the subsequent melee both are disordered

Combat on the German left flank

On the German right flank, the German light infantry advance to within missile range of the Roman light infantry; the Roman light infantry retire.

Light infantry get to fire at the oncoming German light infantry.

The Roman cavalry in the woods could just sit there and get fired at by the German light infantry so they charge into them.  Both light infantry fire is ineffective and are disordered in the ensuing melee.

Roman cavalry in the woods charge the German light infantry.

The warbands charge at the Roman infantry – no roll required as they are impetuous and within charge range of the Romans.  The warband unit on the German far right charged a light infantry unit that managed to disorder the Warband as they were charging.

Warbands charge

The Warbands rolled really well (three 6x out of 6 rolls!) and they are tripled in combat value for the first melee.  They manage to disorder a few legionary units and rout an Auxilia unit.

The Warbands don’t break the line but cause a lot more disorders that they received in return.

It is the Romans turn and the legions that are disordered are not going to attack as it will be at 1:1.  The legion units with the General can attack as they are doubled in combat value.

Note that melee is optional so if combat values are equal, such as disordered Auxilia Vs disordered cavalry on the Roman right, then if there is an equal chance of routing each other (both are already disordered so a 1d6 for melee sees a 1 = attacker routs,  6 = defender routs) you would not do so unless tactically there is a greater reward than the risk of combat. Short answer is the Auxilia are not going to melee the German cavalry.

Legions fight back – one warband lost (on the right)

The Roman cavalry in the woods rout the opposing light infantry.  They have been really lucky with the die rolls are the cavalry are half combat value in the woods.

Roman cavalry in the woods are victorious over the German light infantry.

On the German turn the warbands are at a disadvantage now (combat value 2 Vs disordered Roman legion value of 3).  It is a stalemate so time for the risk Vs reward I discussed earlier.  If the German cavalry can rout the Auxilia (need to roll a 6) they open up the left flank and can attack the flank of the Roman line.  They roll a 6!
German left flank cavalry in melee with the Roman Auxilia.  Germans rout the Auxilia.

Germanicus (Roman leader) routs an opposing warband unit. 

And does it again

The German cavalry moves and charges the Roman legion in the flank.  It has a leader so will be difficult to rout.  Did nothing.

German cavalry on the flank of a legionary unit.

The Roman Cavalry in the woods charges a German warband and manages to rout it!

Roman cavalry in the woods charges at a German warband that is routed in the resulting melee

The Warbands are stuck – they cannot attack anywhere at 1:1 odds, the minimum required that has a chance of destroying a unit. Warbands are value 2, disordered heavy infantry is 3. The Romans are less stuck as they can attack the Warbands at 1:1 but do have a equal chance of themselves routing.  But they are further away from their breakpoint than the Germans (one more warband gone and the Germans lose, compared to the Romans can lose 3 more units).  Time is running out.  The Romans attack the warbands in the centre, disordered them and then roll a 6 to rout one.  They do no manage to rout a unit themselves.

Roman legionaries and German Warbands fight it out.

The Romans win!

End game, Romans win.

Rule changes

None, although leaders in Bill Banks Ancients represent army capability as leaders are removed and added where required.  When you make them permanently attached to units they make those units very powerful.  I do remember toning them down in a previous version of When Worlds Collide to +1 to CV rather than a x2 modifier.  I may still do this but not yet – see how it goes in more battles.  In the above battle the German cavalry should have bypassed the legion with the leader for one without a leader.

Also, I am changing doubling for a flank attack to triple.  A flank attack at the moment at x2 is the same as defneding terrain or a leader attached.  I believe they should be far more decisive - a German Heavy Cavalry on the flank of an ordinary Roman legion should not be 1:1 or worse.

Light infantry and light cavalry do not have a fire and retreat reaction in these rules when charged.  They used to in my other rules. They either fire or retreat (or do nothing).   After about 5 games so far it has not been a problem but we shall see.  For light infantry it has been fine so far but I have not used much light cavalry in any of the games.


Got to test out a lot of the rules and it all hung together fine.  It was going to be hard pressed for the Germans to win this one.  They did get some lucky rolls but once the first change was done allthey could hope for was a draw.


  1. Shaun, a good test, with a scenario that offers enough variables to give the rules a fair run. I would agree with the triple of a flank attack value for the reasons you state … or maintain a doubling and always ignore defensive terrain.

    I would also put a question mark on whether Roman cavalry would be so effective in woods.

    I’m sure this is a battle covered by the Great Battles in History boardgames series. I will check that out.

    1. Hello Norm

      Good point - the cavalry should not have been effective as it was - can't even follow my own rules! Cavalry in woods are disordered (basically 1/22 strength) but I had them ordered and full strength. Ah well :-)

  2. Thanks Shaun, that is another set of Ancients rules for me to try out.

    1. lol. Focus on Phalanx :-) These are not there yet, not too much testing happened yet.

  3. Close but not quite for the Germans.

    1. If the Germans had just managed to rout one or two legionary units when they first charged the Roman line it would have been a different outcome.

  4. Shaun - In retrospect what difference would if have made if the Roman cavalry had been (correctly) disordered?
    TBH I don’t have very much experience riding horses, but I always preferred clear, open ground. Sure, you can ride (walk) horses through woods but I would be apprehensive about riding fast - branches hanging down, uneven ground, limited visibility for both horse and rider.
    Still, as long as you are making progress…

    1. If the cavalry were disordered the initial attack onthe light infantry would have been at 1:1 rather than 2:1, and the attack on the flank of the warband would have also been at 1:1, not 2:1. 1:1 has equal chance of damage to either side, while 2:1 you inflict damage on a 3-6.

  5. I appreciate the authenticity and sincerity in your writing.