After toqui Ainavillo's defeat in the Battle of Andalien he gathered tens of thousands of warriors from the Arauco and Tucapel regions to reinforce his depleted 15,000 man army for an attack on Valdivia's new settlement at Penco. Meanwhile Valdivia's force took eight days to construct a fort with a circuit of 1500 paces around his new settlement with a ditch 12 feet deep and wide. The excavated earth was used to fill in behind a wall of tree trunks driven into the earth above the ditch. It had three gates with well built bastions provided with artillery. Following the construction of the fort, Valdivia established the city of Concepción del Nuevo Extremo there on March 3, 1550. He also sent out patrols of his cavalry to call on the local Mapuche to submit to Spanish rule and provide food a