Battle of Chacabuco

In January 1817 José de San Martín led around 4,000 men over the high Andes from Argentina in a crossing planned for years. The Spanish scattered their forces to cover every pass and then concentrated on the ridge at Chacabuco. San Martín attacked in two columns, with Bernardo O'Higgins's column advancing early and a second column arriving to complete the encirclement. The royalists broke and Santiago opened its gates to the victors.

The battle is often presented as the finish of a flawless plan, but the two columns did not arrive in perfect synchrony, and O'Higgins's decision to attack early has been argued over by Chilean and Argentine historians for two centuries. The crossing itself, with mules, guns and thousands of men over passes above 3,000 metres, was the larger achievement, and its losses of animals and equipment were heavy. Royalist forces returned in 1818 and the decisive battle came at Maipú.