In 1560, a thousand Spanish conquistadors, and a score of captured Indians, march down from Quito in the Andes mountains into the jungle below. Under the command of Gonzalo Pizarro, the party's mission is to find El Dorado. The men, clad in half armor, pull cannons through narrow mountainous paths and hot, thickly humid jungle. After much difficulty, Pizarro orders a small expeditionary group of forty men to continue ahead by rafting a river.  If they do not return to the main party within one week with news of what lies beyond, they will be considered lost. Pizarro chooses Don Pedro de Ursúa as the leader of the exploratory team. Don Lope de Aguirre is named second-in-command. One of the four rafts becomes separated from the others and gets caught in an eddy.  A rescue team is unable to approach the raft until the following day, when all men on the raft are discovered killed by unknown attackers.