▁that ▁they ▁could ▁be ▁easily ▁destroyed . ▁ ▁The ▁Bir ch ▁Cou lee ▁cam ps ite ▁was ▁not ▁easily ▁def ens ible , ▁since ▁the ▁Indians ▁could ▁approach ▁from ▁all ▁sides ▁and ▁still ▁remain ▁under ▁cover . ▁Also , ▁since ▁the ▁bur ial ▁detail ▁felt ▁themselves ▁safe , ▁they ▁did ▁not ▁take ▁pre ca utions ▁against ▁attack ▁such ▁as ▁dig ging ▁ent rench ments ▁and ▁posting ▁sent ries ▁far ▁enough ▁from ▁camp ▁to ▁give ▁am ple ▁warning . ▁ ▁During ▁the ▁night , ▁Gray ▁Bird , ▁along ▁with ▁chief s ▁Red ▁Leg s , ▁Big ▁E agle , ▁and ▁M ank ato ▁crossed ▁the ▁Minnesota ▁River ▁and ▁surrounded ▁the ▁camp . ▁In ▁the ▁morning , ▁the ▁Indians ▁comm enced ▁their ▁amb ush , ▁w ounding ▁at ▁least ▁thirty ▁United ▁States ▁soldiers ▁and ▁killing ▁most ▁of ▁the ▁caval ry ' s ▁horses ▁within ▁the ▁first ▁few ▁minutes . ▁The ▁heav iest ▁part ▁of ▁the ▁fight ▁last ed ▁about ▁an ▁hour , ▁but ▁the ▁sie ge ▁continued ▁for ▁many ▁hours ▁past ▁then . ▁Colonel ▁S ible y ▁could ▁hear ▁the ▁sounds ▁of ▁the ▁battle ▁from ▁Fort ▁R id g ely , ▁about ▁six teen ▁miles ▁away , ▁so ▁he ▁sent ▁out ▁a ▁relief ▁party ▁of ▁ 2 4 0 ▁men . ▁Colonel ▁Mc Ph ail , ▁heading ▁up ▁the ▁relief ▁party , ▁thought ▁he ▁was ▁almost ▁completely ▁surrounded ▁by ▁the ▁Si oux ▁and ▁sent ▁back ▁for ▁more ▁rein for c ements . ▁S ible y ▁returned ▁with ▁more ▁rein for c ements ▁and ▁an ▁art