He was appointed by Pedro de la Gasca, the "Peacemaker," to found the city to commemorate the peace in the Peruvian colonies after the defeat of the Pizarro brothers.

Mendoza's life took another dramatic turn when he decided to serve under the orders of Pedro de la Gasca, the envoy of the King, who entrusted him with a group of chivalry in the battle of Sacsahuaman.

On 7 April 1548 de la Gasca notified Captain Mendoza that he was appointed to found a new city to commemorate the victory of the royal forces and the peace.

Many members of the staff of the Viceroyalty of Peru, many commissioners and soldiers, priests and traders were familiar with a valley known as Chukiyawu, next to the Illimani mountain, and knew that there was a small Indian village.

Nuestra Señora de La Paz became part of the route that connected Lima to Potosí, the city built around the richest silver mine in the world.

– A commemorative statue in honor of Alonso de Mendoza can be seen in La Paz, in the site where he founded the city, known then by the natives as Churupampa (Field of Shells).