José de San Martín's Army of the Andes begins crossing the Andes

Background. The Crossing of the Andes was a significant feat in the Argentine and Chilean wars of independence. The idea originated with secret lodges and the Maitland Plan. Following the defeat at Rancagua in 1814, Chile became a royalist stronghold, prompting leaders like Bernardo O'Higgins to flee to Mendoza. San Martín, as governor of Cuyo, organized the army in Mendoza to invade Chile.

Preparation. San Martín developed a plan to defeat Spanish forces using an alternative path to Peru, avoiding Upper Peru. The army was not ready in summer 1815, delaying the crossing. By the end of 1816, the Army of the Andes comprised 5,000 men, 10,000 mules, and 1,500 horses. A report detailing the military plan was submitted to the Supreme Director in autumn 1816.

Execution. On January 19, 1817, San Martín and his army departed from El Plumerillo. The crossing took 21 days, covering 500 kilometers of mountain range. The army successfully entered Santiago, Chile, on February 13, 1817. This operation was supported by guerrilla activities in Santiago by Manuel Rodríguez, who had returned before the crossing.