When Hernan Cortez, clanking and sweating and swearing in his heavy armor, aided by thousands of Indian allies, destroyed the Aztec capital of Tenochitlan on August 13, 1521, he shattered the entire Aztec Empire.
Uncertain of what this triumph meant in this new world of unknown size, population and nature, Cortez immediately sent two lieutenants, Francisco Montando and Cristobal de Olid, westward to begin reconnaissance—wherever conquest and pacification were not possible.
These expeditions were the beginning of the 1521-1525 exploratory “campaign” that would eventually reach the Pacific Ocean. By the end of 1521, Montaño’s men were the first Europeans to reach Mechuacan (today’s Michoacan, Jalisco’s neighboring state). This early penetration of the fiercely independent Purépecha Kingdo —it had defeated several attempted invasions by Aztec armies—was followed by Cortez’s cousin, Captain Pedro Alonzo de Avalos, sent to find a way to the East Indies. Both parties heard stories of a vast body of water to the west. Some said it was a lake, or a sea, or an ocean.
Spanish outriders pushing beyond the Purépecha capital of Tzintzuntzan quickly ran into what they did believe was the Pacific Ocean. Instead, it was a giant lake, which they called El Mar Chapalico.
Much of this history, cluttered and often contradictory, was recorded after the fact, frequently by differing pious chroniclers, most of whom wished to produce a tidy version of events. Despite that, historians agree that a large expedition of conquistadores led by Alonzo de Avalos “pacified” the region embracing the western swing of the Chapalico Sea by 1524.