It was established on May 14, 1769, by Gaspar de Portolá, leader of the first European land exploration of Alta California—at that time an unexplored northwestern frontier area of New Spain.

[2] Prior to occupation by the Spanish, the site of the Presidio was home to the Kumeyaay people (called the Diegueños by the Spaniards).

The first Europeans to explore San Diego Bay and its environs were members of the maritime expedition led by Juan Rodríguez Cabrillo in 1542.

On July 16, 1769, Mission San Diego de Alcalá was established by Junípero Serra on Presidio Hill.

The presidio had a commanding view of San Diego Bay and the Pacific Ocean, allowing the Spanish to see potential intruders.

In 1907, George Marston, a wealthy department store owner, bought Presidio Hill with an interest to preserve the site.