April 5, 1818

Battle of Maipú

Battle of Maipú: San Martín's United Army defeats Osorio near Santiago

At six in the evening San Martín wrote from the field that his cavalry was still chasing the fugitives, and declared: "La Patria es libre."

Cerrillos del Maipo, 5 April 1818

On 5 April 1818 the combined Chilean–River Plate United Army, commanded in the field by José de San Martín, met Mariano Osorio's Royalist army at Cerrillos del Maipo, south of Santiago.

The Patriot force stood at about 5,400 men with 21 guns at the start of April, rebuilt and rearmed after Osorio had surprised and dispersed it at Cancha Rayada on 19 March.

San Martín deployed divisions under Gregorio de Las Heras and Rudecindo Alvarado, with Hilarión de la Quintana holding the reserve.

The reserve sent obliquely

When Alvarado was pushed back, San Martín sent the reserve obliquely to support him while Las Heras kept up pressure on the other flank.

The Royalist line broke and withdrew toward the Lo Espejo estate. Osorio escaped; José Ordóñez carried on the final resistance there and was captured.

The cavalry officer Santiago Bueras was killed while his horsemen attacked and dispersed the Royalist cavalry.

What the dispatch says, and what it doesn't

At 6 p.m. San Martín reported more than 1,500 prisoners, the capture of the Royalist artillery and cavalry still in pursuit.

He said only that Patriot deaths were "very few," which does not support the precise casualty totals often attached to the battle; recent archaeological-historical research argues the combined death toll may have been below 1,000.

Bernardo O'Higgins, still recovering from a wounded arm, reached the field near the end with roughly 1,000 more men and met San Martín there in the encounter remembered as the Abrazo de Maipú.

Sources

Researched 24 Aug 2026 7 sources not yet audited

How this was checked

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What the sources leave uncertain

Published army strengths and casualty totals vary considerably by source and by whether late arrivals are counted.
San Martín's same-day dispatch is strong evidence for more than 1,500 prisoners but says only that Patriot deaths were “very few”; it does not support the article's precise casualty totals.
Recent archaeological-historical research argues that the combined death toll may have been below 1,000, substantially lower than traditional accounts.