 Faced with these constraints , the Spanish expedition had to cross the river several times and fight at each ford against stiff opposition . The bulk of the Inca army confronted the Spaniards from a set of terraces overlooking a plain by the Urubamba River . Several Spanish assaults against the terraces failed against a shower of arrows , slingshots and boulders coming down from the terraces as well as from both flanks . To hinder the efforts of the Spanish cavalry the Incas flooded the plain using previously prepared channels ; water eventually reached the horses ' girths . The defenders then counterattacked ; some of them used Spanish weapons captured in previous encounters such as swords , bucklers , armor and even a horse , ridden by Manco Inca himself . In a severely compromised situation , Hernando Pizarro ordered a retreat ; under the cover of darkness the Spanish force fled through the Urubamba valley with the Incas in pursuit and reached Cusco the next day . 
