Copiapó. The whole of the north of Chile was in the power of the invaders.
On that same 12th February Freyre, at the other extreme of the line of operations, occupied the city of Talca, after a skirmish on the plains, cutting all communication between the capital and the south. He represented himself to be the vanguard of the main army, and was joined at once by the Chilian guerillas and by Neyra.
It was only on the eve of departure that San Martin explained his plan in its entirety to his generals. On the 18th January Las Heras marched with a flying column by Uspallata, with instructions to entrench himself at Chacabuco, but to retreat if attacked by superior forces. Two days in his rear marched Beltran with the artillery. The main body marched on the 19th by Los Patos; the vanguard was commanded by Soler, and one day's march in his rear came the reserve under O'Higgins. Groups of pioneers preceded the columns, clearing the way for them. Soler had instructions to debouch on the 8th February into the valley of Putaendo, to seize the bridge which crosses the river Aconcagua in front of the town of San Felipe, to occupy that position, thence to open communications with Las Heras, and, if possible, to attack the enemy in the rear at Santa Rosa.
All the troops were mounted on mules, and marched in single file along the narrow paths, each twenty men being in care of a muleteer, the length of each day's march being decided by the facilities for grass and water at the halting-places. Not only was the road itself by Los Patos more difficult than that by Uspallata, but on account of the greater elevation, and of its vicinity to the eternal snow of the higher peaks, the cold was very much more intense; it freezes hard there every night, even at midsummer, and the rarefaction of the air caused many of the men to drop from the ranks.
Marcó had despatched 1,000 men under Colonel Atero to reconnoitre the pass of Uspallata, and on the 24th January
