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  • Martin Boulter

Clash of Empires Caesar against the Celts Battle of Bibracte July 58 BC

In this article I’m going to use the Clash Battle System to recreate the Battle of Bibracte (58 BC), which was the second major battle of the Gallic Wars 58 – 51 BC. This battle is significant because it illustrates the relentless form of attack of a Roman Legion as represented by the linear exchange of tired engaged troops for fresh men from the rear ranks. This together with the keeping back of a tactical reserve and good leadership enabled the Roman army to consistently defeat vastly larger barbarian armies.


The opening events of the Gallic War took place in the spring of 58 BC in the Roman province of Transalpine Gaul over which Gaius Julius Caesar had just been made proconsul. Probably for personal aggrandizement rather than any real threat Caesar decided to intercept a migratory horde of Gallic peoples the Helvetti and their allies who were heading for the Rhone Valley in southern Gaul. After winning himself time by feigned negotiation Caesar destroyed the one bridge across the Rhone River and fortified the southern bank. Finding their way blocked the Helvetti decided to take an alternative route through the Jura mountains. By the time they had crossed this barrier Caesar had assembled six legions to block their way. A forced march and surprise attack by three of these legions annihilated an advance group of 30,000 Helvetian warriors as they were in the process of crossing the Arar River. After this clash Caesar positioned his army on a plateau (Mount Beuvary) with four of his more experienced legions in three lines on the slopes and his two less experienced legions and auxiliaries entrenched on the summit. The Helvetti and their allies still had about 70,000 warriors and early on a July afternoon they made their attack against the Romans’ elevated position. The Helvetti surged up the slope in a deep mass, but despite the ferocity of their charge they were unable to prevail against the Roman battle tactics. Gradually they were forced back by the Roman legionaries who due to their training and discipline were able to exchange their front ranks for fresh troops from the rear. At this point the armies of the Boii and the Tulingi who were the allies of the Helvetti attacked the Roman right flank. Thereupon Caesar ordered the first and second lines to keep up the pressure on the Helvetti while he detached the third line which was in reserve and turned it to face the new threat. By the end of the day the Gallic warriors had had enough and after a last stand in their camp they were slaughtered. In the violent struggle 130,000 Helvetians including women and children fell. Roman losses were heavy but not known precisely.

Clash of Empires

Using the Clash of Empires rules the battle strength and capabilities of the belligerents can be shown as follows: -

Later Republican Roman Army

The Later Republican Roman army of Caesar consists of 27 units inclusive of cavalry. Following the reforms of Caius Marius, the Roman army is now a professional Standing army which uses 2D10 for its Battle Dice.  A Standing Roman Legionary army has a Combat Rating of and gets +1 to Initiative for Forced March. On the Combat Rating (CR) to Fighting Bonus (FB) Conversion Table a CR of equates to +13 FB for 27 Roman Legionary units. A Standing Roman Legion can save against defeat by rolling 4-6 on 1D6 for Relentless. This can be used for a field battle and once only. If successful, the Roman army can fight again. In this refight any tactical or numerical superiority that either side might have is negated, but the Roman army will get a manipular support bonus of +1D6. If the Romans choose not to refight then they can disengage with 25% losses to the loser and 10% losses to the winner. The Romans also have a Heavy cavalry upgrade which gives them a +1D8 Battle Advantage Die and associated +1 to Initiative for cavalry. At this early stage in his military career Caesar is ranked as competent and rolls 1D6 for Initiative. Therefore, the Later Republican Roman army rolls 1D6 +2 for Initiative. The Roman army is significantly outnumbered by its opponent.

Gallic Army

The Gallic army consists of 56 units inclusive of cavalry. It is a Warband army which uses 2D6 for its Battle Dice and has a Combat Rating of . On the Combat Rating (CR) to Fighting Bonus (FB) Conversion Table this equates to +17 FB for 56 Warband units. Celtic Warbands have a special advantage called Battle Rush which enables them on an odds or evens score on the Battle Dice to gain a +1D6 Battle Bonus and if they win Initiative they can double this bonus i.e., 1D6 x2. Celtic tribes have a standard 1D6 Battle Advantage Die and associated +1 to Initiative for cavalry. The leader of the Gallic host is Divico and he is a competent commander who rolls 1D6 for Initiative. Therefore, the Gallic army rolls 1D6 +1 for Initiative and outnumbers its opponent by more than 2-1 so gets +2D6 Battle Advantage Dice.  

Clash Battle System

After rolling for Initiative the Battle Roll for each army consists of the following procedure: -

  1. Roll Battle Dice (highest scoring die only)

  2. Plus, Combat Rating (CR) to Fighting Bonus (FB) (conversion dependent upon number of units)

  3. Plus, Fighting Technique Battle Bonus (activated by odds or evens Battle Dice)

  4. Plus, Advantage Dice (representing a numerical, tactical or other special advantage)

  5. Highest score wins and the difference between the two Battle Rolls determines the number of casualties.

Battle Log

Later Republican Roman Army


Battle Dice

No. of Units

CR to Fighting Bonus/Battle Bonus if applicable

Battle Advantage Dice

Total Score

1D6 +2 = 6





(Highest die only)


7 and 6


(6 Legions)

x 27 = +13 FB



Relentless 4-6

Saving roll = 4

Heavy Cavalry +1D8

Tactical Advantage +1D6


6 + 2 = 8

7 + 13 + 8 = 28





6 and 4


+13 FB

Heavy Cavalry +1D8

Manipular Support Bonus +1D6


 7 + 4 = 11

6 + 13 + 11 = 30

Note: - The Roman army manages to win Initiative and takes up a position on high ground in three battle lines. The enemy clash violently with the first line and due to the ferocity of their attack and numerical superiority would have won the battle had not the Romans successfully made their Relentless saving roll. This represents the first line when hard pressed falling back to be relieved by the second line and the deployment of the reserve to counter the Gallic flank attack. On the refight roll the Romans score 30. Thus, they win a decisive victory for the loss of 5 units.

Gallic Army


Battle Dice

No. of Units

CR to Fighting Bonus/Battle Bonus if applicable

Battle Advantage Dice

Total Score

1D6 +1 = 5




(Highest die only)


5 and 5


(70,000 warriors)

x 56 = +17 FB



Battle Rush 1D6 (x2)


Light/Medium Cavalry +1D6

Opponent outnumbered more than 2-1 +2D6


3 + 3 + 4 = 10

5 + 17 + 3 + 10 = 35





2 and 3


+17 FB

Light/Medium Cavalry +1D6

= 3

3 + 17 + 3 = 23

Note: - The Gallic army loses Initiative but still manages to activate its Battle Rush with two odd numbers on the Battle Dice. This together with their numerical superiority should have won the battle for them. However, they are undone by the Roman battle tactics and are forced to make a refight roll without the benefit of their more than 2-1 numerical bonus. The result is a catastrophic defeat and the loss of 75% of their army which equates to 42 units.

Caesar’s legions clash with a migratory Gallic horde at Bibracte 58 BC. Figures by Essex and Irregular Miniatures from their 25mm Ancients range. Painted by Silurian and from the author’s own collection. The numerical strength of each army is denoted by the coloured plastic counters. Game board from the Clash of Empires: The Hellenistic World Game.

The imposing Gallic horde crashes into the first line of the Roman army at the Battle of Bibracte 58 BC. Figures by Essex Miniatures from their 15mm Ancients range. Painted by Silurian and from the authors own collection. Army composition calculated by the Clash Conversion Table for Wargaming.


Boulter, M. L. 2009/2024: Clash of Empires: The Hellenistic World. Silurian War Games Ltd.

Dupuy, R. E. and Dupuy, T. N. 1993: The Collins Encyclopaedia of Military History. Harper Collins Publishers.

Hackett, J. 1989: Warfare in the Ancient World. Sidgwick & Jackson Ltd.

Jimẻnez, R. L. 1996: Caesar Against The Celts. Spellmount Limited.

Mellersh, H.E.L. 1995: Chronology of the Ancient World, 10,000 BC – AD 799. Helicon Publishing Ltd.

Article Front Page Picture

Vercingetorix throws down his arms at the feet of Julius Caesar - Lionel Royer, 1899. After Alamy (IY04522604).

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