Wargaming the Battle of Maipo 5 Apr 1818

On 5 Apr 1818, in one of the bloodiest battles in the Wars of South American Independence, the Patriots under San Martin decisively defeated the Royalists under Mariano Osorio. Although I posted a draft of this back in January 2012 I completely updated it so have reposted it.

Historical Situation

Setting: Maipo, South of Santiago, Chile; 5 Apr 1818

The war

Since 1810 the Spanish colonies in South America had embraced open revolution against Spain. The United Provinces of the South ( Argentina and Uruguay ) had actually achieved independence by 1815, but their war against the Royalist forces in the northern territories of Argentina and Bolivia had been unsuccessful. After the defeat of a Patriot army at the battle of Sipe Sipe (or Viluma), the only thing preventing the royalists from regaining control of the River Plate was the guerrilla warfare done by the Gauchos, but the future appeared uncertain.

Back in 1812 a creole career military officer had return to South America after serving Spain in the wars against Napoleon. He was abandoning a promising career in the Spanish military after being promoted for his role as ADC to Coupigny during the battle of Bailen, his new objective was to return to his native land and lead contribute to the Patriot efforts.

By 1817 San Martin had realised that Buenos Aires attempts to defeat the Royalists forces in the north were ill conceived and that the way to achieve this would be to cross the Andes and liberate Chile and from there initiate an amphibious operation to Peru, the heart or the Royalist presence.

With this in mind San Martin gathered an Army and crossed into Chile in early 1817, defeating the opposing forces in Chacabuco. However after the initial victory he had to return to Buenos Aires to secure further resources for the campaign.

While San Martin was in Buenos Aires the war in Chile became more complicated due to the arrival of the “expedicionarios” reinforcements from Peru, which included veteran peninsular units.

Battle of Cancha Rayada

Now in 1818, with San Martin back in Chile, Royalist and Patriots forces were moving towards each other once again.

The Royalists took first blood when on March 19th the Royalist Brigadier Jose Ordonez, a skilful Spanish commander that had been a comrade of San Martin in the peninsular war, convinced the Royalist general, Mariano Osorio, to initiate a night offensive on the Patriot army that had besieged them in the city of Talca. The Patriot army was manoeuvring to prepare themselves for the attack, alerted by spies, but they were caught before they could deploy, this was the battle of Cancha Rayada. The Patriot army routed from the field but calm and ordered performance by Las Heras insured that the main body of the army retreated in good order preventing a total defeat, nevertheless panic spread among the Patriots and morale was very low.

Preparations for battle

A few weeks later San Martin had managed to regroup a good portion of the patriot army and was now ready to face Osorio’s army that was moving towards Santiago. O’Higgins was left in Santiago with some troops fortifying the city in case disaster should occur and the main body of the army left with the Argentine general to face the enemy at a valley close to the river Maipo.

Some of San Martin officers were not very convinced with facing the army that had surprised them at Cancha Rayada in a set piece battle in open terrain; Brayer a French officer in Patriot service requested to be excused and San Martin dismissed him declaring: “The last drummer in the army has more courage than your generalship, you may leave then but you should know that in the next hours the fate of Chile will be decided.”

The troops deploy on the field by around 11:30AM.

The Royalists deployed the Grenadier and Cazadores companies together with 4pdr guns and the Frontier Dragoons on the left flank under command of Primo de Rivera while the fusilier companies and the 8 pdr guns were deployed in the center, anchored on the elite Burgos battalion and with their light dragoons securing their right flank.

San Martin deployed Las Heras division with 3 infantry battalions, Blanco Encalada’s horse artillery and the horse grenadiers to his right facing Primo de Rivera, and Rudecindo Alvarado with another 3 infantry battalions in the centre supported by de la Plaza 8pdr Andes artillery and Brogono’s 4pdr artillery in support with the patriot light cavalry protecting their flank, but he also deployed Hilarion de La Quintana’s division in reserve with another 3 infantry battalions.

The armies were roughly similar in numbers since although the Patriots presented more battalions most of these were understrength not reaching 400 men each while the royalist expeditionary battalions were at full strength of 1000 each.

And so one of the bloodiest battles in the war of Independence was about to begin.

Map / Terrain

To the east, in the Llanos de Maipo, is the main road from Santiago to the south. The Patriots deployed to the north on the large height of the Loma Blanco. The Royalists deployed on a large triangular rise to the south. Further south was the Hacienda de lo Espejo. Several small rises also featured.

Plan of the Battle of Maipo (Barrientos Gutiérrez, 1947, p.72)
Plan of the Battle of Maipo (Barrientos Gutiérrez, 1947, p.72)
Plan of the Battle of Maipo - Cadot
Plan of the Battle of Maipo – Cadot
Plan of the Battle of Maipo - Jose Carlos Astolfi
Plan of the Battle of Maipo – Jose Carlos Astolfi

Pre-game preparation


Royalist Player (Defending)

Deploys first and takes second turn.


Defeat the Patriots.

Forces Available

Royalist Order of Battle

  • Brigadier General Mariano Osorio
  • Colonel Jose Ordoñez
  • Right Division
    • Concepcion Battalion
    • Infante Don Carlos Battalion
    • Lanceros del Rey
    • Dragones de Arequipa
    • Foot Artillery [4x8lb]
  • Centre Division
    • Arequipa Battalion
    • 1st Burgos Battalion
    • Dragones de Chillan
    • Dragones de la Frontera
  • Left Division
    • “Reunion of various units”
    • Artillery [4 x 4lb; 4 x 3.5″ Howitzer]

Apparently the orbat John Fletcher included in his Liberators book (2005) started with Pezuela’s Order of Battle before the Battle of Maipo.


Deploy on the large triangular rise and the hills to the north-west.



Patriot Player (Attacking)

Deploys second and takes first turn.


Defeat the Royalists.

Forces Available

I’ve updated the Patriot order of battle from Fletcher (2005). I have:

  • Specified the nationality of all units, in particular the Patriot Artillery.
  • clarified the identify of the various Patriot Cazadores a Caballo.
  • Merged the Chilean Lancers into the Caballeria Cazadores de la Escolta Directorial as they were probably just a company within that unit.
  • Specified the division commanders are specified although they might not have a role within the rules you choose.

Here is the result:

Revised Patriot Order of Battle

  • General San Martin
  • Right Division (Coronel Las Heras)
    • Argentine 11th Infantry Regiment
    • Chilean Coquimbo Cazadore Battalion
    • Chilean Infantes de Patria Battalion
    • Argentine Granaderios a Caballo
    • Chilean Artillery Battery [4×4 lb]
  • Centre Division (Coronel Quintana)
    • Chilean 1st Infantry Battalion
    • Chilean 3rd Infantry Battalion
    • Argentine 7th Infantry Regiment
    • Squadron of the Chilean Caballeria Cazadores de la Escolta Directorial
    • Argentine Artillery Battery [2×8 lb]
  • Left Division (Comandante Alvarado)
    • Chilean 2nd Infantry Battalion
    • Argentine 8th Infantry Regiment
    • Argentine Cazadores de los Andes Battalion
    • Argentine Cazadores a Caballo de la Escolta del General
    • Squadron of the Chilean Caballeria Cazadores de la Escolta Directorial
    • Chilean Artillery Battery [4×4 lb]


Deploy on the slopes of the Loma Blanco.



Victory Conditions

Beating the other army using the appropriate rules from your preferred set of rules.

The Patriots were attacking so need some victory condition incentive to do so. Perhaps the Royalists win on a “draw”.

Scenario Special Rules


Wargaming Challenges

Maipo is a pretty straight forward battle but still offers a few challenges to the wargamer.

Table orientation and size

For me the big question is what table size and orientation to fight the battle. John Fletcher (2005) assumes the battle is fought with the Patriots attacking from the short table edge on a 6’x4′ table. This is at 1:1440 scale (1″ = 40 yards).

My most likely scale is 1:1000 (about 1″ = 30 yards) so I need a much bigger table to refight John’s scenario, with Patriots coming from a short table edge. Here is my map for an 8′ x 5′ table based John’s map and also on the “Plan of the Battle of Maipo” by Cadot that I included above.

Table Maipo 8'x5' 1-1000 Scale Attack from short edge
Table Maipo 8’x5′ 1-1000 Scale Attack from short edge

The trouble is that I don’t own an 8′ x 5′ table. Okay my mate next door does, but my biggest table at the moment is 6′ x 4′. And that makes for quite a different table layout if I retain the 1:1000 scale. Not least the Patriots attack from a long edge and I only show half of the big triangular rise.

Table Maipo 6'x4' 1-1000 Scale Attack from long edge
Table Maipo 6’x4′ 1-1000 Scale Attack from long edge

Actually it would be interesting to try both of these configurations to see if there is a difference.

Equal forces

The armies are about equal yet the Patriots have the obligation to attack. Challenging.

Trudge into artillery

The Patriots, being the attacker, have to trudge between the two hills under cannon fire. Depending on the rules this is quite a challenge; this is exactly the problem we experienced in our trial with the Portable Wargame.

Last stand

Historically the Royalists retreated to the Hacienda of Espejo for their last ditch stand. Most rules will struggle to allow this; the army is likely to break and flee the field as a group.

Scenarios, Games and Battle Reports

Available scenarios and battle reports:


Barrientos Gutiérrez, P. (1947). “Historia del Estado Mayor del Ejército”. Instituto Geográfico Militar, Santiago.

Fletcher, J. (2005). Liberators! Volume 1: The War in the South. Grenadier Productions.

Marley, D. (1998). Wars of the Americas: a chronology of armed conflict in the New World, 1492-1997 [2nd ed.].

1 thought on “Wargaming the Battle of Maipo 5 Apr 1818”

  1. That’s really well done indeed. Apart from needing a tennis court for a table, I’d be interested to see how this battle could be represented in 28mm. My rules of choice for this battle would be “General de Brigade.” Must agree though that John Fletcher is a great source for scenarios for these wars.


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