The Repository Códice

San Martin Told the Enemy Which Pass He Would Use

September 13, 2026 · Runtime 11:35 · Watch on YouTube

On the day the battle for Chile was decided, the Spanish governor had about 4,317 soldiers and brought roughly 1,500 of them to the field. Nothing had happened to the rest. They were standing guard along a front of nearly a thousand kilometres, because of something San Martin had arranged to have said out loud, fifteen months earlier, to two thousand people on the other side.

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Transcript

The rest were standing guard 0:00

On the twelfth of February, eighteen seventeen, the Spanish governor of Chile had about four thousand three hundred soldiers. He brought fifteen hundred of them to the battle that decided the country. Nothing had happened to the others. They were not dead and they were not lost. The rest were standing guard, along a front of nearly a thousand kilometres. They were waiting for an attack that never came there.

The other half of the operation 0:27

The crossing of the Andes is the part that gets remembered. Five thousand people and ten thousand animals, over passes above three thousand metres. This episode is about the other half of the operation. It ran for fifteen months before anyone started walking, and its weapon was a rumour.

Five hundred kilometres of cordillera 0:47

The problem was shaped by the mountains. Between the Argentine province of Cuyo and the Chilean central valley lie more than five hundred kilometres of cordillera. There are only a handful of usable passes, and an army coming from the east has to commit to one of them weeks in advance. The defender does not have to be clever. He only has to guess right once.

The man doing the guessing 1:11

The man doing the guessing was Francisco Casimiro Marco del Pont, captain general of Chile since December of eighteen fifteen. His forces were later counted at four thousand three hundred and seventeen men. On paper that is enough to hold a mountain range. In practice it is only enough if you know which part of it to hold.

The war of the sap 1:33

What San Martin ran against him has a name in the Spanish sources. It is called the guerra de zapa, the war of the sap. The word is borrowed from siege engineering, where the sap is the tunnel dug under a wall. It was proclamations, false news and rumours, pushed into Chilean society through agents. The same agents came back carrying the other half: positions, routes, and the state of the royalist garrisons.

Two hundred men, three thousand tied down 2:02

The man who ran it inside Chile was a Santiago lawyer named Manuel Rodriguez. Popular memory made him an insurrection. The records make him something smaller and more interesting. His bands never passed two hundred men, and they were closer to bandit parties than to an army. Those two hundred were enough to keep three thousand royalist soldiers tied down between the Aconcagua and the Maule.

The door of the governor's carriage 2:29

The point was never to win anything. It was to make the government in Santiago feel surrounded. Rodriguez raided towns, circulated proclamations, and at one point held open the door of the governor's own carriage for him. A governor being shown that he is not safe in his own capital makes decisions about where to put soldiers.

An envoy with a document nobody wanted 2:51

The second operation was quieter, and it produced the single most valuable object of the whole campaign. In eighteen sixteen San Martin sent an officer to Santiago as an envoy. He carried a copy of the declaration of independence signed at Tucuman on the ninth of July.

Alvarez Condarco, and his memory 3:10

The envoy was Jose Antonio Alvarez Condarco, from Tucuman. He ran the army's powder works, and he had an unusual visual memory for terrain. Delivering the document was the excuse. Reading the road was the assignment.

Out by Los Patos, home by Uspallata 3:27

San Martin sent him out by the pass of Los Patos, which is the longer and harder of the two northern roads. Marco del Pont received him, refused the document, and sent him home the way a governor gets rid of an inconvenient visitor. He sent him back by Uspallata, because Uspallata is shorter.

Maps drawn under the enemy's passport 3:47

So Alvarez Condarco crossed the cordillera twice, by two different passes, within a few weeks. He was not carrying paper. He memorised the valleys, the gorges and the turns, and he drew them when he got back. The maps that took the Army of the Andes into Chile were made under a passport signed by the man they were used against.

San Carlos, 30 September 1816 4:11

The third operation is the one this episode is about, and it happened in the open. On the thirtieth of September, eighteen sixteen, at the fort of San Carlos in southern Mendoza, San Martin held a parliament with the Pehuenche. Two thousand of them came. He asked for permission to take his army across their land, and for two hundred guides.

There is no picture of that day 4:34

There is no picture of that day. Nobody at San Carlos drew the meeting, and no image of it entered any archive. What the archive has is the same people, on the same side of the same mountains, drawn a few years later by travellers who went through. That is what you are looking at, and it is worth saying out loud.

Who had spoken to them first 4:55

Now the part that makes this a plan rather than a courtesy. The Pehuenche were not neutral, and San Martin knew it. Two and a half years earlier, in February of eighteen fourteen, a Spanish brigadier had held his own parliament at Chillan. It sealed an alliance with them. They were counted by the royalists as their own.

A meeting is not a secret 5:18

So a meeting with two thousand people from the other side is not a secret negotiation. It is a broadcast. The historians who study this list the parliament as part of the guerra de zapa, not as something happening beside it. One of the chiefs carried the news across the mountains, which is what news does.

Why the story was believable 5:38

And the news was believable, which is the part that is easy to miss. The southern passes are lower and gentler than the northern ones. Crossing there is the sensible plan. Marco del Pont already suspected the attack would come from the south. What arrived from the Pehuenche did not change his mind. It confirmed it.

A defence spread over a thousand kilometres 6:01

The result is the number this episode opened with. The royalist forces in Chile stayed divided until very shortly before the invasion. Two thousand around Santiago, five hundred at Concepcion, two hundred at Coquimbo. The rest sat in detachments strung along a colony that is far longer than it is wide.

January 1817 6:22

The army moved in January of eighteen seventeen. Roughly four thousand regular soldiers and twelve hundred militia, raised in a province of three small towns. It did not cross by one road, and it did not cross by two. It crossed by six.

The two that carried the war 6:41

Two of the six carried the war. The main column went by Los Patos, under San Martin himself, with O'Higgins, Soler and Zapiola. Two thousand six hundred and fifty fighting men, and seven guns. The second went by Uspallata under Las Heras, six hundred and eighty men. They met again in the Aconcagua valley.

The other four 7:05

The other four were small, and they were far away. Zelada crossed at Come Caballos with two hundred men and reached Copiapo. Cabot crossed at Guana with a hundred and forty and reached Coquimbo. Lemus took fifty-five over the Portillo, south of Santiago. Freire took a hundred over the Planchon, and marched south first to hide where he was going.

Four hundred and ninety-five men 7:30

Put those four together and you get four hundred and ninety-five men, out of the roughly three thousand eight hundred who marched. Thirteen per cent of the army, sent over four separate passes, hundreds of kilometres apart, with no way of supporting each other or anyone else. As a military operation that is indefensible. As the last chapter of a rumour it is exact.

What the mountain took 7:54

The crossing itself was as hard as the monuments say. One count of the animals lists seven thousand three hundred and fifty-nine riding mules and one thousand nine hundred and twenty-two pack mules. Another thousand went with the southern detachments, and a second account puts the number leaving Mendoza near nine thousand eight hundred. About four thousand three hundred mules reached Chile.

Three thousand metres, and higher 8:19

The horse figures are worse and less certain. Sources give between twelve hundred and sixteen hundred setting out. Around five hundred arrived. The losses go down to the ground, the lack of water and forage, and the weather of the high mountains. The routes averaged three thousand metres, and in places passed four and a half thousand.

The mountain was the price, not the plan 8:43

All of that is true, and none of it defeated anybody. No royalist soldier was beaten by an altitude. What beat the defence of Chile was that on the day the army came down into the Aconcagua valley, most of that defence was somewhere else. The mountain was the price of the plan. It was not the plan.

Chacabuco, 12 February 1817 9:04

On the twelfth of February the two main columns met the royalists at the Chacabuco ranch, north of Santiago. San Martin had around three thousand five hundred men on the field. The royalist commander, Rafael Maroto, had about fifteen hundred.

The order that fixed the number 9:22

Maroto knew the arithmetic. He had proposed falling back to the Maule river and joining the forces from Concepcion before fighting anything. The governor agreed, then changed his mind, and ordered him to stop the invaders short of Santiago. So fifteen hundred men stood where four thousand should have been, because of a decision made about a pass in the south.

As the patriot report filed it 9:46

The patriot report gives twelve dead and a hundred and twenty wounded on its own side. On the royalist side, five hundred dead, and thirty-two officers and six hundred soldiers taken prisoner. Other accounts describe the first charge being thrown back with heavy losses, so the twelve is best read as the figure the winners filed.

The part the monument leaves out 10:08

And here is the part the monument leaves out. The victory was not followed up. The beaten royalists were allowed to reach the coast, and about sixteen hundred of them re-embarked for Peru. Those men became the core of the expedition that came back the following year. Historians have argued ever since that Chacabuco should have ended the war.

A date, a place, and two thousand people 10:31

The crossing has monuments on both sides of the border. It has a national holiday in Argentina. It is the image every schoolbook uses. The parliament at San Carlos has none of that. It has a date, a place, and a count of two thousand people who were told something specific so that they would repeat it.

Nobody is ready everywhere 10:52

What that meeting bought was not surprise. Marco del Pont knew an army was coming. What it bought was that he had to be ready everywhere, and nobody is ready everywhere. The two hundred guides he asked for that day are not named on any panel.

Fifteen months past Chacabuco 11:09

Manuel Rodriguez, who ran the war of the sap inside Chile, lived fifteen months past Chacabuco. In May of eighteen eighteen, with the war won, his own side took him out of Santiago under escort. He was shot in the back on the road. Five years later the officer guarding him named who gave the order. Next episode: the file on that killing.

Description and sources

The crossing of the Andes in January 1817 is the image every schoolbook uses: five thousand people and around ten thousand animals over passes averaging three thousand metres, some above four and a half thousand. About 4,300 of the roughly 9,300 mules reached Chile, and around 500 of the 1,200 to 1,600 horses. All of that is true, and none of it beat anybody.

What beat the defence of Chile was an operation the Spanish sources call the guerra de zapa - the war of the sap, named for the tunnel dug under a besieged wall. It ran from 1815 to 1817: proclamations, false news and rumours pushed into Chilean society through agents, and the same agents coming back with positions and routes. Inside Chile it was run by a Santiago lawyer, Manuel Rodriguez, whose bands never passed two hundred men and were enough to keep three thousand royalist soldiers tied down between the Aconcagua and the Maule.

Two operations decided the campaign. The first was an envoy: Jose Antonio Alvarez Condarco, sent to Santiago in 1816 with a copy of the Tucuman declaration of independence as his excuse. San Martin sent him out by the hard northern pass of Los Patos; Marco del Pont, getting rid of him, sent him home by the shorter Uspallata. He carried no paper and drew both roads from memory when he got back. The maps that took the army into Chile were made under a passport signed by the man they were used against.

The second happened in the open. On 30 September 1816, at the fort of San Carlos in southern Mendoza, San Martin held a parliament with two thousand Pehuenche and asked permission to take his army across their land, and for two hundred guides. The Pehuenche were not neutral: two and a half years earlier a Spanish brigadier had sealed an alliance with them at Chillan, and the royalists counted them as their own. A meeting with two thousand people from the other side is not a negotiation. It is a broadcast - and the southern passes it pointed at are the lower, easier ones, which made the story the sensible plan rather than a suspicious one.

The army then crossed by six passes. Two carried the war: Los Patos with 2,650 fighting men under San Martin, O'Higgins, Soler and Zapiola, and Uspallata with 680 under Las Heras. The other four - Come Caballos, Guana, the Portillo and the Planchon - carried 495 men between them, thirteen per cent of the army, spread over hundreds of kilometres with no way of supporting each other. As a military operation that is indefensible. As the last chapter of a rumour it is exact.

At Chacabuco on 12 February 1817, San Martin put around 3,500 men on the field against roughly 1,500. Rafael Maroto had asked to fall back to the Maule and join the forces at Concepcion first; the governor agreed and then reversed it. The part the monument leaves out is what happened after: the victory was not followed up, and about 1,600 beaten royalists re-embarked for Peru and became the core of the expedition that came back the following year.

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