Mancera Island (Spanish: Isla Mancera) is a minor island at the mouth of Valdivia River. It was named after the Spanish viceroy of Peru Pedro de Toledo, 1st Marquis of Mancera, who fortified the island. The fort was a vital point in the Valdivian Fort System, preventing enemy ships from reaching Valdivia from Corral Bay. In 1682, after Valdivia was badly damaged by a fire it was proposed to move the city to Manrcera Island. A similar proposal of moving the city to Mancera Island was done in 1721 in order to protect it against a potential British attack as Spain and Britain were at war.