The modern city began as a mining town, officially founded as Villa de Durango by Francisco de Ibarra on July 8, 1563. Ibarra was sent north by Viceroy Luis de Velasco to conquer the territory and found the city. The site was chosen because of its proximity to the Cerro de Mercado, thought at the time to contain reserves of silver, but instead was found to be an important source of iron. The mountain was named for Captain Ginés Vázquez de Mercado, who discovered the valley on his expeditions in the north. The site was also chosen because it was close to the Franciscan mission at Analco, which was a source of water, wood and animals to hunt. The initial layout of the town was done by Alonso de Pacheco, bordered by what are now Madero and Constitución streets on running north–south, and by 5 de Febrero and 20 de noviembre running east–west. The historic center is still centered by the Plaza de Armas (main square) and the Cathedral Basilica.