San Martin's Crossing of the Andes (1817) and Chacabuco

San Martín’s crossing of the Andes was the march of the Army of the Andes over the mountain passes between Mendoza, in present-day Argentina, and Chile in January and February 1817. Led by General José de San Martín, about 5,000 soldiers crossed some of the highest passes in the Americas and surprised the Spanish royalists, defeating them at the Battle of Chacabuco on 12 February 1817. The campaign restored Chile’s independence movement and became one of the great military feats of the Spanish American wars of independence.

Background

The independence movements in Spanish South America began after Napoleon’s invasion of Spain in 1808 left the Spanish crown in crisis. In Buenos Aires the May Revolution of 1810 created a local government, and Chile set up its own governing junta in September 1810.

By 1816 the cause was in danger. Royalist armies from Peru, the strongest Spanish base in South America, had defeated several patriot expeditions into Upper Peru (modern Bolivia). In Chile the patriots were crushed at the Battle of Rancagua on 1–2 October 1814, and their leaders, including Bernardo O’Higgins, fled across the mountains to Mendoza. Spain restored royal rule in Chile, a period Chileans call the Reconquista.

José de San Martín, born in 1778 in Yapeyú in the Río de la Plata region, had served for over 20 years in the Spanish army, including against Napoleon’s forces. He returned to Buenos Aires in 1812 to join the independence cause. He became convinced that the way to defeat Spain was not through Upper Peru but by crossing the Andes to free Chile and then attacking Lima by sea.

Building the Army of the Andes

In 1814 San Martín became governor of Cuyo, the province around Mendoza. Over more than two years he turned the region into a military base. Taxes, donations and forced loans paid for the army; workshops under the friar Luis Beltrán made cannon, ammunition and equipment; and a camp at El Plumerillo trained recruits. Chilean exiles joined, and many soldiers were freed slaves, who formed important infantry battalions.

Support came from Juan Martín de Pueyrredón, who became supreme director of the United Provinces of the Río de la Plata in 1816, the year the provinces declared independence at Tucumán on 9 July. San Martín also ran a campaign of spies and false information, the guerra de zapa, to mislead the royalist governor of Chile, Francisco Casimiro Marcó del Pont, about which pass he would use. Partisans led by Manuel Rodríguez raided inside Chile to spread confusion.

The crossing

The army set off in mid-January 1817. It numbered roughly 5,000 men, about 4,000 of them combat troops, with around 10,000 mules, 1,600 horses, herds of cattle and around 20 pieces of artillery. Supplies included dried meat, onions and garlic, believed to help against altitude sickness.

The main body under San Martín, with divisions led by Miguel Estanislao Soler and O’Higgins, took the long Los Patos route to the north. A second column under Juan Gregorio de Las Heras, carrying most of the artillery, used the shorter Uspallata pass. Smaller detachments crossed far to the north, towards Copiapó and Coquimbo, and to the south, so that Marcó del Pont spread his forces thinly to guard many possible routes.

The route climbed to well over 4,000 metres at its highest points, by most estimates around 4,500–4,800 metres, with freezing nights, thin air and narrow trails above steep drops. Soldiers suffered from cold and altitude sickness, and many animals died; estimates suggest that roughly half the mules and most of the horses were lost. Human losses were relatively small given the conditions. The columns descended into Chile in early February almost exactly as planned, a remarkable feat of coordination across widely separated routes.

The Battle of Chacabuco

Marcó del Pont gathered what troops he could near the Chacabuco hacienda, north of Santiago, under Brigadier Rafael Maroto. San Martín planned a double attack on 12 February 1817: O’Higgins was to hold the royalists’ attention from the front while Soler’s division moved round their flank.

O’Higgins attacked earlier than intended and came under heavy pressure, but Soler’s arrival on the royalist flank and a cavalry charge broke Maroto’s line. Royalist losses are usually given as about 500 killed and 600 captured, while patriot losses were around 12 killed and roughly 120 wounded, though figures vary between sources. Marcó del Pont fled and was captured on his way to the coast.

Consequences

The patriot army entered Santiago on 14 February 1817. An assembly offered San Martín the leadership of Chile, but he declined, and O’Higgins became supreme director on 16 February. Chile formally declared independence on 12 February 1818, the first anniversary of Chacabuco.

Royalist forces still held the south, around Talcahuano. A royalist army from Peru surprised the patriots at Cancha Rayada on 19 March 1818, but San Martín won the decisive Battle of Maipú on 5 April 1818. Chile then built a navy, and in 1820 San Martín’s expedition sailed to Peru, beginning the campaign that ended Spanish rule in South America at Ayacucho in 1824.

Legacy

The crossing is celebrated in both Argentina and Chile, and San Martín is honoured as the Liberator of Argentina, Chile and Peru. Military historians admire the campaign for its planning, logistics and deception rather than for a single battle. Re-enactments are held in the Mendoza region each summer, and the Army of the Andes is a central story in Argentine national history.

Key people

José de San Martín planned the campaign in detail and personally crossed with the main column, despite poor health. Bernardo O’Higgins, the son of an Irish-born viceroy of Peru, led a division and became Chile’s head of state after the victory. Miguel Estanislao Soler commanded the vanguard whose flank attack decided Chacabuco, and Juan Gregorio de Las Heras brought the artillery safely through Uspallata. Fray Luis Beltrán, a Franciscan friar turned military engineer, ran the arsenal and devised ways to haul cannon over the passes. On the Spanish side, Governor Francisco Casimiro Marcó del Pont was outmanoeuvred, and Rafael Maroto, who later became a general in the Carlist wars in Spain, commanded at Chacabuco.

By the numbers

Figures are estimates from the army’s records and later histories, and vary between sources.

Timeline

• 1814, 1–2 October: Chilean patriots defeated at Rancagua; exiles flee to Mendoza.
• 1814: San Martín becomes governor of Cuyo and begins building an army.
• 1816, 9 July: Congress of Tucumán declares the independence of the United Provinces.
• 1817, mid-January: Army of the Andes leaves Mendoza in several columns.
• 1817, early February: Columns descend into Chile.
• 1817, 12 February: Battle of Chacabuco; royalists defeated.
• 1817, 14 February: Patriot army enters Santiago.
• 1817, 16 February: Bernardo O’Higgins becomes supreme director of Chile.

Why it matters

The crossing of the Andes turned the tide of the independence wars in southern South America. By freeing Chile, San Martín gained a base, a navy and allies for the attack on Peru, and his strategy linked the independence of three nations.