In 1483, the Portuguese explorer Diogo Cão sailed up the uncharted Congo River, finding Kongo villages and becoming the first European to encounter the Kongo kingdom. Cão left men in Kongo and took Kongo nobles to Portugal. He returned with the Kongo nobles in 1485. At that point the ruling king, Nzinga a Nkuwu, converted to Christianity. Cão returned to the kingdom with Roman Catholic priests and soldiers in 1491, baptizing Nzinga a Nkuwu as well as his principal nobles, starting with the ruler of Soyo, the coastal province. At the same time a literate Kongo citizen returning from Portugal opened the first school. Nzinga a Nkuwu took the Christian name of João I in honor of Portugal's king at the time, João II.