BC (for "Before Christ") is an abbreviation used to refer to a year before the beginning of the yearcount that starts with the supposed year of the birth of Christ.
Some people use ACN or BCE instead.
See also AD and CE.
... Amazon, the largest river in the world by volume, the Parana[?] with its impressive Iguaçu[?] falls, the Rio Negro, São Francisco[?], Xingu, Madeira and the Tapajós[?] ...