Isabel Barreto de Castro (Pontevedra, Galicia, Spain), (1567 – 1612) was a Spanish sailor and traveler, the first known woman to hold the office of admiral in European history. She was purportedly the granddaughter of Francisco Barreto, governor of Portuguese India. Isabel Barreto married Alvaro de Mendaña, Spanish navigator, patron of several expeditions to the Pacific Ocean, and European discoverer of the Solomon Islands and the Marquesas Islands.
Isabel accompanied her spouse on his last expedition from Peru to the Pacific. In the Santa Cruz Islands, she replaced Mendaña and her brother, Lorenzo Barreto, as Adelantada and Governor after their death. She and the main pilot Pedro Fernández de Quirós arrived at Manila, in the Philippines, with the 100 survivors of the expedition in the only remaining ship (at the beginning 378 men and women in four ships), after a terrible voyage of twelve weeks from the settlement of Santa Cruz (Nendö).
Doña Isabel was honoured in Manila, and Quirós was commended for his service; with both absolved of any responsibility for the results of the expedition. Isabel, accused of cruelty by the crew, demonstrated a strong personality with great leadership and great determination. She had an uncompromising attitude and managed to maintain severe discipline of the crew of tough and adventurous men, always willing to conspire and mutiny.
She remarried to general Fernando de Castro, again crossing the Pacific Ocean to Mexico, and then settled in Buenos Aires, where they lived for several years, before returning to Peru.
It is said that Isabel crossed the Atlantic Ocean for the last time to Spain to defend her rights over the Solomon Islands, because the King had granted the right to colonize the islands to Pedro Fernández de Quirós. She may be buried in Castrovirreyna (Peru) or in Galicia (Spain), in 1612.
Route of Mendaña/Barreto/Quirós 1595 expedition:
The voyage's story is told in The Islands of Unwisdom, an historic novel by Robert Graves.