Meantime Güemes had entered the Sierra to the east of Salta, and on the 9th and 18th, two parties of his Gauchos surprised two detachments of the enemy. On the 29th he came so close to the city that Castro sallied out against him for about a league with eighty men, but was completely routed, with the loss of half his force.
For this feat Güemes was named Commandant-General of the Vanguard, and on the recommendation of San Martin, was raised to the rank of Lieutenant-Colonel.
Güemes then occupied the approaches to the city and harassed the garrison by daily attacks upon the suburbs. Being reinforced from Jujui, the Royalists then organised two expeditions of 500 men each. One, composed of a battalion of infantry and a squadron of light horse under Colonel Alvarez, marched early in June into the valley of Lerma. At the town of Sumalao, Alvarez found the vanguard of the Guachipas awaiting him. The Patriot outposts were driven in, but the main body sheltered by trees and broken ground, poured so heavy a fire upon him that he was forced to return to the city, with many killed and wounded, and with the loss of all the supplies he had seized.
The other column, also composed of infantry and cavalry, was under the command of Colonel Marquiegui, who like Castro was a native of Salta, and of great repute for skill and knowledge of the country. This column marched to the east and was met by Güemes in person, who made so stubborn a resistance that it was also forced back to the city, and the siege was re-established.
Pezuela had drawn in his reserves and advanced to Jujui. Thence he sent orders to Colonel Marquiegui to march with one hundred infantry and one hundred and fifty horse, by the north-eastern frontiers of Tucuman and Santiago del Estero, to the rear of the advanced guard of the Patriots on the river Pasaje. Marquiegui carried out his instructions with great skill, captured several forts, and learned from prisoners that the army of San Martin consisted only of three thousand recruits, and that the vanguard which gave them so much trouble, was nothing but a swarm of undisciplined Gauchos; but he also learned that the object of the campaign, which was the relief of Monte Video, was now impossible, that city having already fallen.
When news of this expedition reached Tucuman, Güemes was immediately reinforced by one hundred infantry and one hundred mounted grenadiers, and Marquiegui retreated, marching one hundred leagues in a semicircle, but was prevented from carrying off either horses or cattle.
This was the last attempt at invasion; five thousand men were not enough to capture Tucuman, much less to conquer the country. Pezuela withdrew his troops beyond the frontier, and sent off a strong detachment to Cuzco to crush an insurrection which had broken out in that city.
The object of the Royalist invasion was, by a powerful diversion, to compel the Argentine Government to withdraw their army from the Banda Oriental for the protection of the northern provinces, but meantime that government had armed and equipped a small naval force, which, under the command of an Irishman named BROWN, had, on the 16th May, defeated and almost destroyed the Spanish squadron stationed at Monte Video, which city soon after surrendered to the Argentine army then besieging it under the command of Alvear.
Before the conclusion of these events, the General of the Army of the North had disappeared from the theatre of war. San Martin, after careful study of the question, had clearly discerned that the road by Upper Peru was not the true strategical line of the South American revolution. His idea was to carry the war to the West, to pass the Andes, to occupy Chile, to secure the dominion of the Pacific, and to attack Lower Peru on the flank, continuing military operations to the North merely as a subordinate detail of the main design.
This plan, the merits of which were not appreciated by his contemporaries until it was crowned with victory, is looked upon by posterity as not merely the most simple, but as the only possible plan which could give the desired result. It was then held to be folly, whilst in reality the folly lay in persevering in the attempt to reach Lima with insufficient means and by an impracticable route. Knowing that it would be looked upon as folly, San Martin kept his idea to himself, as his secret, as he himself styled it in confidential intercourse, waiting to disclose it for the day when he should hold in his hand the thunderbolt which was to shatter the power of Spain in America. Three months after taking command of the Army of the North, he wrote to his friend, Don Nicolas Rodriguez Peña:—