It was then that Arenales marched from Huara on his second expedition to the Highlands. The purpose of this expedition was to hasten the evacuation of Lima and to occupy such positions as would prevent the Royalists from re-establishing themselves in the Highlands; then to open communications at Ica with another expedition, which was sent along the coast southwards under Miller. For the first of these purposes the guerillas, guarding the passes from Lima, were instructed to obey all orders received from Arenales. In case of disaster, Arenales was instructed to retire on the reserve stationed at Huaylas.

The division of Arenales consisted of 2,200 men, the column under Miller of 600, thus San Martin was left with about 3,000 sick and convalescent in front of the Royalist Army of 7,000.

The troops sent with Arenales, worn out by the endemic fevers of the coast, were more like spectres than men, so that the first movements of the expedition were very slow. The Cordillera was crossed by the Oyon Pass on the 6th May. The heights were covered with snow and the cold was intense. Aldao with the remnants of his division led the van. Pasco was occupied on the 11th, and Carratala retired precipitately. Tarma and Jauja were taken on the 20th and 23rd, and Carratala continuing to retreat, the valley of Huancayo lay open to the Patriots on the 25th.

Arenales now prepared for a vigorous attack upon Carratala, when advice reached him of the signing of the armistice of Punchauca, which put a stop to operations for the present, retired to Jauja and employed himself in reorganizing his force, now swelled by recruiting to over 4,000 men.

Arenales was a peculiar character. Austere and subtile, his military ideas were as conspicuous for foresight as for audacity, while his every act was inspired by a sense of justice and duty. He was very strict with his subordinates, who both feared and respected him. He went about attended only by an orderly, had only one spare charger and one baggage mule. He himself saddled and unsaddled his horse, and shod him himself also. He mended his own boots and uniform, and was so careless of dress that San Martin at times had his valise replenished for him, unknown to him. On the march he carried his own provisions in his saddle-bags—a cheese and a piece of cold beef. San Martin styled him “Mi compañero,” and was more familiar with him than with any one else. He responded by exact obedience to orders, but did not scruple to criticise them whenever he thought proper.

From Jauja Arenales wrote San Martin, earnestly impressing upon him the advisability of transferring his whole force to the Highlands, leaving Lima to be watched by the fleet, but at the conclusion of the armistice he resumed operations by marching against Canterac, who had passed the Cordillera, when, on the 12th July, he received a despatch from San Martin, ordering him to retire on Pasco or on Lima, if menaced by the enemy.

Arenales saw clearly that this movement would entail the destruction of his division; he had heard of the evacuation of Lima, but knew nothing of the movements of La Serna. In his perplexity he called a council of war, at which it was decided to retire to Huancayo.

This movement was the salvation of Canterac, who had lost so heavily on the march from Lima, that he reached Huancavelica with only 1,500 starving men. La Serna, marching on Jauja, found the passes occupied by the mountaineers, who rolled great rocks down the mountain slopes upon his troops, so that, after heavy loss, he was forced to retreat, after throwing several guns into the river. Then following the route previously taken by Canterac, he joined him on the 4th August, the united force numbering barely 4,000 men, of whom many were sick.

At Huancayo Arenales found that Vidal and his guerillas had withdrawn to Lima, on which he continued his retreat to Jauja. Thence he wrote again to San Martin, showing him how the occupation of Lima would be as disastrous to the Patriot as it had been to the Royalist army, but in obedience to orders continued his retreat, losing hundreds of his new recruits by desertion.

Again he wrote to San Martin, proposing a new plan of campaign, which would compensate for the loss of the Highlands. The answer he received was an order to continue his retreat to Lima.