▁had ▁a ▁gap ▁in ▁his ▁line . ▁In ▁moving ▁units ▁to ▁shore ▁up ▁the ▁supposed ▁gap , ▁Rose cr ans ▁accident ally ▁created ▁an ▁actual ▁gap , ▁directly ▁in ▁the ▁path ▁of ▁an ▁eight - br ig ade ▁assault ▁on ▁a ▁narrow ▁front ▁by ▁Confeder ate ▁L t . ▁Gen . ▁James ▁Long street , ▁whose ▁corps ▁had ▁been ▁det ached ▁from ▁the ▁Army ▁of ▁Northern ▁Virginia . ▁In ▁the ▁resulting ▁rout , ▁Long street ' s ▁attack ▁drove ▁one - third ▁of ▁the ▁Union ▁army , ▁including ▁Rose cr ans ▁himself , ▁from ▁the ▁field . ▁ ▁Union ▁units ▁sp ont ane ously ▁r al lied ▁to ▁create ▁a ▁def ensive ▁line ▁on ▁H ors es ho e ▁R idge ▁(" S n od gr ass ▁Hill "), ▁forming ▁a ▁new ▁right ▁wing ▁for ▁the ▁line ▁of ▁Maj . ▁Gen . ▁George ▁H . ▁Thomas , ▁who ▁assumed ▁overall ▁command ▁of ▁remaining ▁forces . ▁Although ▁the ▁Confeder ates ▁launched ▁cost ly ▁and ▁determined ▁assault s , ▁Thomas ▁and ▁his ▁men ▁held ▁until ▁tw il ight . ▁Union ▁forces ▁then ▁retired ▁to ▁Ch att ano oga ▁while ▁the ▁Confeder ates ▁occupied ▁the ▁surrounding ▁height s , ▁bes ie ging ▁the ▁city . ▁ ▁Background ▁ ▁Military ▁situation ▁▁ ▁In ▁his ▁successful ▁Tul lahoma ▁Camp aign ▁in ▁the ▁summer ▁of ▁ 1 8 6 3 , ▁Rose cr ans ▁moved ▁sout heast ▁from ▁Mur fre es bor o , ▁Tennessee , ▁out man eu ver ing ▁B rag g ▁and ▁forcing ▁him ▁to ▁abandon