Portuguese ships reached the mouth of the Congo in 1483, and in 1491 the king Nzinga a Nkuwu accepted baptism. His son, who took the throne in 1509 as Afonso I and ruled for more than thirty years, made Catholicism the religion of the state: churches were built at the capital, which was renamed Sao Salvador, Kongolese students went to Lisbon and Rome, and in 1518 Afonso's son Henrique was consecrated a bishop, the first from sub-Saharan Africa. Afonso's surviving letters to the Portuguese crown, written in his own chancery, are among the earliest African documents of their kind and include repeated protests at the traders who were depopulating his kingdom.
The Christianity that resulted was Kongolese. Wyatt MacGaffey's work on BaKongo religion sets out the cosmology it met: a world divided between the living and the dead by a boundary often figured as water, a cross of four moments through which the sun and the soul pass, and objects charged for particular purposes. Kimpwanza, the cross form, was already meaningful before a crucifix arrived, and Kongolese crucifixes cast in brass, with an African Christ, were used as emblems of chiefly office as well as of faith.
Whether this was Christianity understood in Kongolese terms or Kongo religion reorganised around Christian symbols is argued, and Kimbwandende Kia Bunseki Fu-Kiau's writing from inside the tradition emphasises the coherence of the older cosmology.