After the blockade had continued for some time, during which the Spaniards made several unsuccesful sallies with considerable loss, Reynoso determined to abandon the fort and to retire with his remaining garrison to Puren, as provisions began to fail, and there was no prospect of being relieved.  Accordingly the whole garrison mounted their horses at midnight, and rushing suddenly from the gate, made their escape through the middle of their enemies.  As the Araucanians supposed this to have been one of the ordinary sallies, they took no measures to obstruct their flight, and Reynoso got off with his men.  Having destroyed the fort of Arauco, Caupolican led his army to attack that of Tucapel, which was commanded by Martin Erizar with a garrison of forty men.  Erizar defended himself gallantly for several days; but as provisions began to fail, and his small force was continually diminishing by the perpetually renewed assaults of the enemy, he likewise determined upon withdrawing to Puren, which he successfully executed, either by similar means as those pursued by Reynoso, or in consequence of a capitulation with Caupolican.  Having destroyed this fortress, Caupolican encamped with his army in the neighbourhood, to wait the approach of the Spaniards, who he supposed would not be long of coming against him with an army.

Valdivia, who then resided in the city of Conception, no sooner learnt that the Araucanians had besieged Arauco, than he began his march for that place with such forces as he was able to collect at a short notice; though contrary to the advice of his most experienced officers, who urged him to wait till he could collect a more formidable army, and seemed to have a presentiment of the fatal consequences which were to result from the present expedition.  The historians of the times differ materially in their accounts of the force under Valdivia on this occasion.  According to some of these his army consisted of two hundred Spaniards and five thousand Promaucian auxiliaries, while others reduce the number to a half.  The same uncertainty is to be found respecting the number of the enemy, some estimating them at nine and others at ten thousand men[68].  On approaching the encampment of Caupolican, Valdivia sent forwards a detachment of ten horsemen under Diego del Oro to reconnoitre, all of whom were slain by the enemy, and their heads cut off and hung upon trees by the way in which the Spanish army had to advance.  On arriving at this place, the Spaniards were filled with horror at this miserable spectacle, and many of them, in spite of their usual intrepidity, were eager to retreat till a greater force could be collected.  Even Valdivia regretted that he had not conformed to the advice of his older officers; but encouraged by the boasting confidence of others, who proudly declared that ten Spaniards were sufficient to put the whole Araucanian army to flight, he continued his march and came in sight of the enemy on the 3d of December 1553.  The prospect of the ruins of Tucapel and the well regulated array of the adverse army, with the insulting taunts of the enemy, who upbraided them as robbers and impostors, filled the minds of the Spaniards, hitherto accustomed to respect and submission from the Indians, with mingled sentiments of dread and indignation.