San Martin Crosses Andes: Chile Liberated at Chacabuco

Five thousand men, 10,000 mules, 1,600 horses, and 600 head of cattle climbed into the Andes in January 1817, crossing passes as high as 12,500 feet through freezing temperatures and thin air, in what military historians rank alongside Hannibal’s Alpine crossing as one of the greatest mountain marches in the history of warfare. Jose de San Martin’s Army of the Andes descended into Chile and destroyed the Spanish royalist forces at the Battle of Chacabuco on February 12, 1817, liberating the country in a single afternoon. San Martin had been planning the crossing for two years from his base in Mendoza, Argentina. He understood what other revolutionary leaders had not: Spain could not be defeated by fighting in each colony separately. His strategy was continental — cross the Andes into Chile, liberate it, then sail north to attack the royalist stronghold in Peru. He spent months gathering intelligence, spreading disinformation to confuse the Spanish about which pass he would use, and training his army for mountain warfare. The crossing itself was brutal. San Martin divided his forces into six columns entering through different passes to prevent the Spanish from concentrating their defense. The main columns crossed in six days, losing hundreds of men, a third of the horses, and half the mules to altitude sickness, cold, and exhaustion. The soldiers chewed garlic and onions to combat the thin air. When the army emerged from the mountains, the Spanish garrison at Chacabuco was caught off guard. The battle lasted less than two hours. Royalist casualties exceeded 500 killed and 600 captured, against fewer than 150 patriot losses. San Martin entered Santiago to cheering crowds and installed Bernardo O’Higgins as Supreme Director of Chile. The crossing of the Andes turned South American independence from a series of local revolts into a coordinated continental war that Spain could not win.