The founding of the Ateneo de Manila University has its roots in the history of the Society of Jesus (Jesuits) as a teaching order. The first Spanish Jesuits in the Philippines, Alonzo Sánchez and Antonio Sedeño, arrived in 1581 as missionaries. They were custodians of the "ratio studiorum", the Jesuit system of education developed around 1559. Within a decade of their arrival, Sedeño and the Jesuits had founded the Colegio de Manila ("Colegio Seminario de San Ignacio") in Intramuros, the historic core of Manila in 1590. The Colegio formally opened in 1595, the first school in the Philippines.