The native inhabitants of that part of the country which formed the territory of Conception, were indignant at being again subjected to the intolerable yoke of the Spaniards, and had recourse to the Araucanians for protection. Caupolican, who seems at this time to have remained in almost entire inaction, either ignorant of the proceedings of the Spaniards, or from some other cause of which we are not informed, immediately sent Lautaro at the head of two thousand warriors to the assistance of the distressed natives on the north side of the Biobio. The young vice-toqui, exasperated at what he called the obstinacy of the Spaniards in rebuilding the city which he had destroyed, immediately passed the Biobio, and the Spaniards imprudently awaited him in the open plain, confiding in their own valour and arms, despising the superior numbers of the barbarians. The Spaniards, however, were panic struck at the furious energy of the first encounter, and fled with precipitation to take shelter behind their ramparts; but were so closely pursued by Lautaro and his valiant followers, that they were unable to close the gate. The Araucanians entered the city along with the fugitives, many of whom were slain; and the small remnant made a precipitate retreat, part of them by embarking in a ship then in the port, and others by taking refuge in the woods, whence they returned through bye-paths to St Jago.
Lautaro immediately plundered and burnt the city, and returned loaded with spoils to his usual station on the mountain of Mariguenu. The successful issue of this enterprise excited Caupolican to resume the sieges or blockades of Imperial and Valdivia, during which Lautaro undertook to make a diversion of the Spanish forces, by marching against St Jago, by which he expected to prevent them from sending reinforcements into the south, and he even conceived that it might be possible to gain possession of that capital of the Spanish dominions in Chili, notwithstanding its great distance; as the successes he had already obtained so filled his mind with confidence that no difficulty appeared too great to be overcome. In order to execute this hazardous enterprise, which appears to have been concerted with Caupolican, he only required five hundred men to be selected by himself from the Araucanian army; but so many pressed to serve under his victorious standard, that he was obliged to admit an additional hundred. With this determined band of six hundred warriors, he traversed all the provinces between the rivers Biobio and Maule, without doing any injury to the natives, who hailed him as their deliverer from the Spanish tyranny. But on crossing the latter river, he immediately proceeded to lay waste the lands of the Promaucians, who were detested by the Araucanians for acting as auxiliaries to the Spaniards. Had he treated them with kindness, he might in all probability have detached them from the Spanish interest and united them in alliance with his own nation. But impelled by eagerness for revenge, he did not appreciate the good effects which might have flowed from a reconciliation with that numerous and warlike nation, whom he considered as traitors to the common cause. Having satiated his revenge, he fortified himself in an advantageous post in their territory on the banks of the Rio-claro, probably on purpose to gain more correct information respecting the state of the city he intended to attack.
This ill-judged delay was of great importance to the inhabitants of St Jago, by giving them time to prepare for their defence. They could not at first believe it possible that Lautaro would have the audacity to undertake a march of three hundred miles beyond the Araucanian frontiers to attack their city; but undeceived by the refugees from Conception, and the daily reports of the ravages of the enemy in the territories of the Promaucians, they dispatched Juan Godinez with an escort of twenty-five horse into the Promaucian country to watch the motions of the enemy, and to send intelligence of his proceedings and designs. Godinez was unexpectedly attacked by a detachment of the Araucanians, and obliged to make a precipitate retreat to St Jago, with his numbers considerably diminished, and filled the capital with consternation and dismay at the intelligence of the near approach of their redoubted enemy. On this occasion the Araucanians took ten horses and some arms from the Spaniards, both of which were used by them in the succeeding actions.
Villagran, who was at this time unable to take the field in consequence of illness, sent his son Pedro against Lautaro with such troops as could be procured, and immediately proceeded to fortify all the approaches to the city of St Jago with strong entrenchments. In the mean time, young Villagran attacked the Araucanians in their fortified post. Instructed by their intrepid yet wary commander, the Araucanians pretended to take flight after a short resistance; but the Spaniards were no sooner entered into the abandoned inclosure, than they returned upon them with such impetuosity, that Pedro and his men were completely routed, and only the cavalry was able to escape by flight, all the infantry who had penetrated the Araucanian camp being put to death. After procuring reinforcements, young Villagran returned three several times to attack the camp of Lautaro, in all of which attempts he was repulsed with considerable loss. He now encamped his force in a low meadow on the banks of the river Mataquito, at no great distance from the entrenched post of Lautaro. The Araucanian general formed a plan for inundating the camp of the Spaniards during night, by turning upon them a branch of the river; but the Spaniards being informed of this design by a spy, withdrew to St Jago.
Having recovered from his illness, Villagran was solicited by the citizens of St Jago to exert himself to dislodge the Araucanians from their neighbourhood, as they every moment expected to see them at their gates. He accordingly, some time in the year 1556, set out from the city at the head of 196 Spaniards and 1000 Indian auxiliaries, in search of Lautaro. Instructed by his severe defeat at Mariguenu, Villagran resolved to attack the enemy by surprise; and quitting the direct road, he secretly directed his march towards the Araucanian encampment in the night by a private path under the guidance of a spy, and reached their entrenchments undiscovered at day-break. Lautaro, who had been on guard all night according to his usual custom, had just retired to rest when the alarm was given of the attack from the Spaniards. He hastened immediately to the spot, to observe the enemy and to issue his orders for defence; but at the moment of his arrival, a dart from the hand of one of the Indian auxiliaries pierced him to the heart. Encouraged by this fortunate event, which was soon known to the Spaniards, Villagran urged the assault of the entrenchments, and soon forced an entrance in spite of the Araucanians, who made an obstinate defence. Finding their post carried, the Araucanians retired to an angle of their works, determined rather to allow themselves to be cut in pieces than to surrender. In vain the Spanish commander repeatedly offered quarter; they continued fighting with the utmost obstinacy till every man of them was cut off, many of them even throwing themselves on the lances of the Spaniards, as if courting death in preference to submission. This victory, which was not obtained without considerable loss on the part of the Spaniards and their allies, was celebrated in St Jago and the other Spanish settlements with every demonstration of joy. The Spaniards felicitated themselves on being freed from a redoubted enemy, who at the early age of nineteen had already obtained so many victories over them, and who threatened to destroy their settlements in Chili, and even to harass them in Peru.