Cartas is the usual designation of a two-volume collection of Jesuit public letters and reports about Japan published in 1598.
Cartas que os padres e irmãos da Companhia de Jesus escreverão dos reynos de Japão e China, t. 1 : aos da mesma Companhia da India e Europa, Vol. I-II, Evora, 1598. (Letters written by the fathers and brothers of the Society of Jesus in the kingdoms of Japan and China.) Volume I is 1549-1580.
They have been translated into Japanese, most recently in Jesuit Reports.