 Virtually all that is known about Kongo in the time of Afonso's reign is known from his long series of letters, written in Portuguese, primarily to the kings Manuel I and João III of Portugal.The letters are often very long and give many details about the administration of the country.Many letters complain about the behavior of several Portuguese officials, and these letters have given rise to an interpretation of Afonso's reign as one in which Portuguese interests submerged Afonso's ambitions.