Acapulco (äkˌəpŏlˈkō) [key], city (1990 pop. 515,374), Guerrero state, S Mexico, on the Pacific coast. A fashionable international seaside resort during much of the 20th cent., it became popular with Mexican vacationers beginning in the late 20th cent. Its natural harbor, surrounded by cliffs and promontories, was a base for Spanish exploration of the Pacific and was key in trade with the Philippines; the city was founded in 1550. The Spanish built (1614) the San Diego fort to guard the harbor. Today tourism and related industries dominate the economy, and workers' hill towns have expanded on its periphery. Acapulco has suffered frequent earthquake and hurricane damage.