 In 1571 Spanish Conquistadors arrived from Mexico , from across the Pacific , and founded present @-@ day Manila in what today is Intramuros . Spanish missionaries soon Christianized the city and incorporated Tondo under Manila and then built some of the oldest churches in the country , including San Agustin Church . The Conquistadors renamed the area Nuevo Reino de Castilla ( New Kingdom of Castille ) and shortened the name to Manila . 
