On abandoning the sieges of Imperial and Valdivia, Caupolican went to join Lautaro at Conception, in order to attempt some enterprise against the Spaniards more practicable than the attack of fortifications, for the assault of which the Araucanians possessed no sufficient arts or arms. Availing himself of the absence of his redoubted enemy; Villagran, who appears to have gone along with the succours to Imperial, ravaged the whole Araucanian territory around that city, burning and destroying the houses and crops, and carrying off all the provisions that were not destroyed to the town. Though of a humane and generous disposition, averse from the exercise of violence, Villagran endeavoured to vindicate the employment of these rigorous measures by the necessity of circumstances, and the pretended rights of war: But on this occasion they were of no real service to the Spanish cause, which they contributed to render more odious to the Araucanians; and in general the only effect which such barbarous conduct produces, is to heap distress on the weak and helpless. To the other terrible calamities inseparable from war, especially when carried on in this barbarous manner, a pestilential disease was superadded which committed dreadful ravages in Chili, especially among the natives. During the incursions of Villagran into the Araucanian territory, some Spanish soldiers, who were either infected at the time or had recently recovered from the small pox, communicated that fatal disease for the first time to the Araucanians, among whom it spread with the more direful and rapid destruction, as they were utterly unacquainted with its nature. So universal and dreadful was the mortality on this occasion in several provinces, that, in one district containing a population of twelve thousand persons, not more than a hundred escaped with life. This pestilential disorder, which has been more destructive than any other to the human race, had been introduced a few years before into the northern parts of Chili, where it then occasioned great mortality among the natives, and where it has since frequently reappeared at uncertain intervals, and has greatly diminished the aboriginal population. For more than a century, counting from the present times, 1787, the southern provinces of Chili forming the Araucanian confederacy, have been exempted from the ravages of this cruel disease, in consequence of the most rigorous precautions being employed by the inhabitants to prevent all communication with the infected countries, similar to those used in Europe to prevent the introduction of the plague.

"The following anecdote will shew what horror the small-pox has inspired into the natives of Araucania. Some considerable time ago71, the viceroy of Peru sent as a present to the governor of Chili, several jars of honey, wine, olives, and different seeds. One of these jars happened to break while landing, and some Indians who were employed as labourers on this occasion, imagined that the contents of the jar were the purulent matter of the small-pox, imported by the governor for the purpose of being disseminated among the Araucanian provinces, to exterminate their inhabitants. They immediately gave notice to their countrymen, who stopped all intercourse with the Spanish provinces and flew to arms, killing above forty Spaniards who were then among them in the full security of peace. To revenge this outrage, the governor marched with an army into the Araucanian territory, and a new war was excited which continued for some time to the great injury of both nations."

While Villagran was using every possible exertion to maintain the Spanish power in the south of Chili, by combating the brave and victorious Araucanians, he found himself on the point of being compelled to turn his arms against his own countrymen. It has been already mentioned that Valdivia, in the instructions he left with the magistrates of Conception before his fatal expedition into Araucania, had nominated Francisco Aguirre in the second place as his own successor in the government, and that Villagran, only third in nomination, had succeeded to the command in consequence of the absence of the other two who were prior to himself. When Aguirre, who was then in Cujo, where he does not appear to have effected any thing of importance, was informed of the death of Valdivia, and his own destination to the government of Chili, he considered the assumption of the vacant command by Villagran as prejudicial to his own just rights, and immediately returned into Chili with sixty men who remained of his detachment, determined to acquire possession of the government by force or favour. His pretensions and those of Villagran must infallibly have kindled a civil war among the Spaniards in Chili, to the ruin or vast detriment of the Spanish interest, had not the competitors agreed to submit the decision of their respective claims to the royal audience at Lima, which at that time, 1555, held the supreme legal jurisdiction over all the Spanish dominions in South America. On this appeal, the court of audience thought proper to set aside the pretensions of both competitors, and issued an edict authorizing the corregidors of the different cities to command each in their respective districts, till farther orders. Perceiving the extreme inconvenience that must have necessarily resulted to the interests of the colony, from this divided government, especially during so important a war, the principal inhabitants remonstrated against the impolicy of this decree. The royal audience listened to the representations of the colonists, and appointed Villagran to resume the command, but only granted him the title of corregidor, and gave him orders to rebuild the city of Conception. Although convinced of the inutility of this measure in the present conjuncture, Villagran, in obedience to the orders, proceeded immediately to that place with eighty-five families, whom he established there, and erected a strong fortification for their defence.

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.