Valdivia, satisfied with his acquisitions, retraced his steps, and on his return march erected a fortress in each of the three provinces of _Puren_, _Tucapel_, and _Arauco_. Without reflecting on the enormous extent of country which he had to defend with so small a force, he on his return to _St. Iago_ despatched Aguirre, with two hundred men, to conquer the provinces of _Cujo_ and _Tucuman_ on the eastern side of the _Andes_. In the province of _Encol_ Valdivia founded his seventh and last city, to which he gave the name of the _City of the Frontiers_, an appellation which, although he could not have foreseen it, is singularly applicable to the position of its ruins to-day, situated as it is on the frontier of _Chili_ and the _Argentine Republic_. On his return to _Conception_ he sent Alderete to Spain with a large sum of money and an account of his conquests. He was to solicit for him in return the perpetual government of the conquered country, with the title of Marquis of _Arauco_.
Whilst Valdivia was employed in maturing his extensive plans, which included the opening up of a direct communication with Europe by way of the Straits of _Magellan_, there was a leading mind at work on the side of the Araucanians with a view to thwarting the schemes of the governor of _Chili_. An aged _Ulmen_ of the province of _Arauco_, named Colocolo, having quitted his retirement, traversed the Araucanian provinces, inciting his countrymen to zeal towards the deliverance of their country. As a practical step towards this end, he implored them to make choice of a new general to replace the dilatory Lincoyan. The age and experience of Colocolo gave him weight with his countrymen; and, accordingly, the _Ulmenes_, who were already of his opinion, assembled to deliberate concerning the election. There were many competitors for the office of general; but all at length concurred in the selection of Colocolo, which fell upon the _Ulmen_ Caupolican, an officer whose subsequent career fully justified the choice.
The new general having assumed the axe which was the badge of his authority, immediately appointed as officers to serve under him each one of his competitors, and even his predecessor. The Araucanians had such confidence in their new _Toqui_ that they clamoured to be led at once against the Spaniards; but their chief repressed this ardour until they should be in a suitable condition to meet them in the field. When they were so, he commenced his operations by a stratagem which was suggested by an accident. A party of eighty natives, allies of the Spaniards, were conducting forage to the neighbouring post of _Arauco_. For these, who fell into his hands, Caupolican substituted a similar number of his own men, whom he directed to keep their arms concealed in the bundles of grass, and to take possession of the gates of the fortress until he should come to their assistance. The stratagem succeeded so far that the guard was surprised and disarmed. The remainder of the garrison, however, succeeded in driving out the Araucanians and raising the drawbridge just as their countrymen approached. The fortress was then attacked, but unsuccessfully, when Caupolican determined to reduce the place by famine.