The Orhon River (old Turkish Orkhon, also Orchon) is a river in Mongolia. It rises in the Hangayn mountains and flows northwards into Lake Baikal. There are two sets of ancient ruins along the river valley: Khara Balgassoun , the ancient capital of the Uighur Kingdom and Khara Horin , the ancient capital of the Mongol Empire. Archaeologists have found several Hunnic Imperial tombs in the area of the river valley.