The soldiers under Valdivia became wearied and disgusted by this continual war, so different from what they had expected; and as they believed him obstinately bent upon adherence to his own plan, and resolved to continue the settlement in spite of every opposition from the natives, they entered into a conspiracy to kill their general and to return into Peru, where they expected to enjoy more ease and tranquillity. Having fortunately got notice of this conspiracy, Valdivia, who possessed great prudence and an insinuating address, soon conciliated those who were least implicated. After this, as he only had the title of general which did not confer any civil and judicial power, he assembled the Cabildo of the city, and persuaded them to invest him in the office of governor of the city and kingdom. In this imposing capacity, he tried and capitally punished some of the ringleaders of the conspiracy, and then prudently exerted himself to soothe the turbulent and seditious spirits of the remainder, by buoying up their hopes with the most flattering promises of future wealth. He had often heard in Peru, that the valley of Quillota abounded in mines of gold, and was hopeful therefore of being able to obtain a sufficient quantity from thence to satisfy the avidity of his soldiers. Notwithstanding the difficulties with which he was surrounded, he sent a party of soldiers into the valley of Quillota, with orders to superintend and protect a number of labourers in digging for the precious metal said to be abound in that place. The mine which was opened upon this occasion proved remarkably rich and productive, surpassing their most sanguine hopes; so that all their past sufferings and present difficulties were soon buried in oblivion, and henceforwards no one had the remotest wish to leave the country. Valdivia, encouraged by this success to new enterprises, ordered a carrack or ship of some considerable size to be built at the mouth of the river Chillan, which traverses the valley of Quillota, for the purpose of more readily obtaining succours from Peru, without which he was fully sensible he could not possibly succeed in the vast enterprise he had in view, which was no less than to accomplish the entire reduction of Chili.
In the mean time, considering the urgent state of his affairs, Valdivia resolved to dispatch two of his principal officers, Alonzo Monroy, and Pedro Miranda by land to Peru, with an escort of six horsemen, whose spurs, bits, and stirrups he directed to be made of solid gold, hoping thereby to entice a sufficient number of recruits to come to his assistance, by this obvious proof of the riches of the country. Although these messengers were escorted to the confines of Chili by thirty additional horsemen, they were attacked and defeated in the province of Copaipo by a hundred archers, commanded by Coteo, an officer of the Ulmen of that province. Of the whole party none escaped with life but the two officers, Monroy and Miranda, who were made prisoners and carried before the ulmen covered with wounds. The prince had resolved on putting them both to death; but, while deliberating on the mode of execution, his wife, the ulmena or princess of Copaipo, moved by compassion for their unhappy situation, successfully interceded with her husband to spare their lives, unbound them with her own hands, tenderly dressed their wounds, and treated them as if they had been her brothers. When they were entirely recovered, she desired them to teach her son the art of riding, as several of the Spanish horses had been taken in the late defeat. The two Spaniards readily consented to her request, hoping to avail themselves of this circumstance to give them an opportunity of recovering their liberty, which they did in effect; but the means they employed was marked by a cruel act of ingratitude to their compassionate benefactress, of so much deeper turpitude that it was unnecessary for their purpose. As the young prince was one day riding between them, escorted by a party of archers and preceded by an officer carrying a lance, Monroy suddenly dispatched him with two or three mortal wounds of a poniard. At the same time Miranda wrested the lance from the officer of the guard, who were thrown into confusion by this unexpected event, and the two Spaniards readily accomplished their escape. Being well mounted, they easily eluded pursuit, and made their way through the desert into Peru, whence they continued their way to Cuzco, where Vaca de Castro then resided, who had succeeded to the government after the cruel assassination of Francisco Pizarro by the Almagrian faction.
When De Castro was informed of the critical situation of affairs in Chili, he immediately sent off a considerable reinforcement by land under the command of Monroy, who had the good fortune to conceal his march from the Copaipans, and to join Valdivia in safety. At the same time the president of Peru dispatched by sea Juan Batista Pastene, a noble Genoese, with a more considerable reinforcement for Valdivia. On receiving these two reinforcements, which arrived about the same time, Valdivia began to carry his great designs into execution. Being solicitous to have a complete knowledge of the sea-coast, he ordered Pastene to explore the whole as far to the southwards as possible, noting the most important places all along the coast; and, on his return from this maritime survey, he sent him back to Peru for additional reinforcements, as the natives had become every day bolder and more enterprising, ever since their victory in Copaipo over Monroy and Miranda. Only a little before this, the Quillotans had contrived to massacre all the soldiers employed at the gold mines in their country, by the following stratagem. One day a neighbouring Indian brought a pot full of gold to Gonzalo Rios, the commandant at the mines, and told him that he had found a great quantity in a certain district of the country which he offered to point out. On this information, all were eager to proceed immediately to the place, that they might participate in the imaginary treasure. As they arrived at the place described in a tumultuary manner and entirely off their guard, they fell into an ambush, by which the whole party was slain, except their imprudent commander and one negro, both of whom saved their lives by the speed of their horses. About the same time the vessel which Valdivia had ordered to be built at the mouth of the river Chillan was burnt by the natives, together with the store-houses or arsenal which he had established in that place.
On receiving notice of the disaster which had taken place at the mines, Valdivia hastened to Quillota with a strong body of troops, and took revenge as far as he could on the Quillotans for the death of his soldiers; after which, he constructed a fort in their country in which he left a garrison for the protection of the people employed in the gold mines. Being soon afterwards reinforced by three hundred men from Peru, under the command of Francisco Villagran and Christoval Escobar, he made choice of a beautiful plain near the mouth of the river Coquimbo, at which place there is a very convenient natural harbour, near which he erected in 1544: a city which he named Serena, to serve as a place of arms to protect the northern part of Chili, and to secure the convoys and reinforcements which might come from Peru in that direction. This place is still known in geography by the name of Serena; but in Chili the native name of Coquimbo prevails, as is the case with most of the Spanish cities and towns in Chili.