The Imperial army reached Mutsu Province and spent several days staying in Koromogawa Village at the entrance of the Isawa where the chieftain Aterui of the Emishi side was based, then after the Emperor Kanmu's reprimand, it took action at the end of June.
陸奥へ達した朝廷軍は、蝦夷側の首領阿弖流爲の根拠地である胆沢の入り口にあたる衣川村に軍を駐屯させて日を重ねていたが、5月末に桓武天皇の叱責を受けて行動を起こした。