Organization
Between 1815 and 1816, Mendoza was practically transformed into a military factory. Its inhabitants participated in the manufacture of gunpowder and ammunition, and learned to make cannons. Expert guides led the army through the mountains. By 1816, General San Martín installed his camp in El Plumerillo, which lay in the northwest of Mendoza Province, 7 km from Mendoza City. San Martín's idea included a complex plan to trick the enemy, spreading rumors that he would cross the Andes by the south, which was the easiest way. The main body of the army crossed the Andes by the difficult passages of Uspallata and Los Patos; they had to travel 500 km through mountain ranges.

Troops and equipment
The Army of the Andes enlisted part of the Army of the North, and a great number of volunteers from Cuyo and former-slaves. They were made up of 5,423 men, who had 22 cannons, 1,129 sabers and 5,000 bayonet guns.

On this occasion, the army used horses and mules. 1,600 battle horses and 10,600 transport mules left the country with the army. Only 800 horses and 3,800 mules returned. It was the first time that the Argentine Army used horseshoes.

The main food of the army was a regional meal called valdiviano. It was prepared with dry meat or charqui, sliced raw onion, and boiling water. The soldiers who carried the food went to rear. They transported 40 tons of charqui, maize cakes, meat, brandy (to counter the nighttime cold), garlic and onion (to deal with the lack of appetite), more than 4,000 cattle for the rest of the campaign, cheese and rum.

The crossing
On January 19, 1817 the soldiers started the crossing. The Army of the Andes left the camp and started the crossing by the passes of Los Patos and Uspallata. These difficult passages, though, ensured the factor of surprise against the enemy. The crossing lasted 21 days.

San Martín's portraitThe plan was to divide the troops in two columns (main and secondary) and four detachments:

Main: led by San Martín, Miguel Estanislao Soler and Bernardo O'Higgins; crossed the Andes by the pass of Los Patos.
Secondary: led by Juan Gregorio de Las Heras, who went through Uspallata.
The main forces reached the other side between 6 and 8 February.

The other detachments were as follows:

A detachment departed from Mendoza led by Lt.-Col. Cabot, with the goal of invading Coquimbo province, in Chile. After promoting popular uprising in the region, Cabot entered triumphantly on February 15.
Manuel Belgrano's army helped with a detachment which had to invade the road of Portillo, from San Juan Province, to the north of Mendoza. 130 men, led by Zelada and Dávila, had to cross the Andes through Guandacol pass. On February 13, Copaipó fell into their hands.
With few men, Captain Lemos had to launch a surprise attack on the guards of San Gabriel on February 4, and pretend that the whole army was invading Chile from the north.
The pass of Planchón was the way taken by Captain General Ramón Freire and his men, who crossed the mountains on February 1.

The Battle of Chacabuco
Main article: Battle of Chacabuco
After the crossing of the Andes, on February 12, the two main bodies of the army, which had travelled through different passages and had met each other in 2 days, attacked and conquered the city of Chacabuco, defeating most of the Spanish forces in Chile. [1]

After the Battle of Chacabuco
Following the liberation of Chile, achieved some months later (see Chilean War of Independence), San Martín's Army Sailed to Peru in order free it and to finally elliminate the possibility of a Spanish attack.

José de San Martín
José Francisco de San Martín Matorras, also known as José de San Martín (25 February 1778 – 17 August 1850), was an Argentine general and the prime leader of the southern part of South America's successful struggle for independence from Spain. Born on February 25, 1778 in Yapeyú, he left his mother country at an early age and studied in Madrid, Spain where he met and befriended Chilean Bernardo O'Higgins. In 1789, after joining the Spanish forces to fight against the French, and participating in several battles such as the Battle of Bailén and Battle of Albuera, San Martín started making contact with South American supporters of independence.

In 1812, he set sail for Buenos Aires from England, and offered his services to the United Provinces of the South (roughly present Argentina). After the Battle of San Lorenzo in 1813, and some time in command of the Army of the North during 1814, he started his plan to attack Lima. This involved first creating an army in Cuyo, liberating Chile, and then attacking Lima by sea.

In 1817, he crossed the Andes from Mendoza to Chile, and prevailed over the Spanish forces after the Battle of Chacabuco and Battle of Maipú (1818), liberating Chile together with Chilean Bernardo O'Higgins. San Martín seized partial control of the viceroyalty's capital (Lima) on July 12, 1821 and appointed Protector of Perú. After a closed-door meeting with fellow libertador Simón Bolívar at Guayaquil, Ecuador on 22 July 1822, Bolívar took over the task of fully liberating Peru and declared its independence. San Martín unexpectedly left Perú and resigned the command of his army, excluding himself from politics and the military, and moving to France in 1824. The details of the 22 July meeting would be a subject of debate by later historians.

Together with Simón Bolívar in the north, San Martín is regarded as one of the Liberators of Spanish South America. He is the national hero of Argentina. The Order of the Liberator General San Martin (Spanish: Orden del Libertador General San Martín) in his honour is the highest decoration in Argentina.

Army of the Andes

The Army of the Andes (Spanish: Ejército de los Andes) was the military force mustered by José de San Martín in his campaign to free Chile from the Spanish Empire. In 1818 it crossed the Andes Mountains from its staging point in Cuyo in the Argentine province of Mendoza, succeeding in its objective by dislodging the Spanish from the country.

When it set out for Chile, the Army was composed of some 4000 soldiers, with 1200 auxileries to help in provisioning and supply. In addition, it had a complement of artillery.

For the crossing of the mountains, the Army was divided into two main columns, the first, commanded by Bernardo O'Higgins, taking the Los Patos Pass and the second, commanded by Juan Gregorio de las Heras, taking the Uspallata Pass. Because this second pass was more negotiable, the artillery was taken in the second column.

Uspallata Pass, through which the second column of the Army of the Andes passed.These two divisions were the main body of the Army, but there were smaller detachments sent to the north and south as flanking wings. The smaller division to the north was composed of some 130 infantry as well as a group of Chilean expatriots, and was under the command of Juan Manuel Cabot. To the south was a group under the command of the Chilean Ramón Freire Serrano.

The Battle of Chacabuco, fought during the Chilean War of Independence, occurred on February 12, 1817. It was a defeat for Spain.

Battle of Chacabuco

The Battle of Chacabuco, fought during the Chilean War of Independence, occurred on February 12, 1817. It was a defeat for Spain.

Background
In 1814, having been instrumental in the establishment of a popularly elected congress in Argentina, Jose de San Martin began to consider the problem of driving the Spanish royalists from South America. He realised that the first step would be to drive them from Chile, and, to this end, he set about recruiting and equipping an army. In just under two years, he had an army of some 6,000 men with 1,200 horses and 22 guns, and, on January 17, 1817, he set out with this force to cross the Andes and liberate Chile. Careful planning on his part had meant that the Royalist forces in Chile were deployed to meet threats that did not exist, and his crossing went unopposed.

The Army of the Andes (as San Martin's force was called) suffered heavy losses during the crossing, losing one-third of its men and more than half of its horses. The Royalist forces had rushed north to respond to their approach, and a force of about 1,500 under Brigadier Rafael Maroto blocked San Martin's advance at a valley called Chacabuco, near Santiago. All he had to do was delay San Martin, as he knew that further Royalist reinforcements were on the way from Santiago. San Martin knew this as well, and opted to attack whilst he still had the advantage of numbers.

The battle
San Martin divided his army into two parts. The first, under General Bernardo O'Higgins, was to fix the attention of the Royalist force to their front, whilst the second, under General Soler, was to move around their left flank. Unfortunately, the flanking force experienced a series of delays, and, as the day wore on, O'Higgins found himself confronting the majority of the Royalist army in an exchange of fire over a deep creek. Taking decisive action (although disobeying orders), O'Higgins ordered a general advance and attacked the Royalist line. The line buckled under the attack, allowing O'Higgins' cavalry to sweep through. The defeated Royalists retreated towards a farm on the vicinity. In the meanwhile, San Martin had personally gone to find the flanking force, and with his arrival turned the Royalist retreat into a rout.

Las seis rutas del cruce de Los Andes: