Nen River
The original seat of the Military Governor of Heilongjiang, as established in 1683, was in Heilongjiang City (also known as Aigun or Heihe, or, in Manchu, Saghalien Ula), located on the Amur River. However, already in 1690 the seat of the governor was transferred to Nenjiang (Mergen) on the Nen River, and, in 1699, further south to Qiqihar. According to modern historians, the moves may have been driven by supply considerations: Nenjiang and Qiqihar are connected by a convenient waterway (Nen River) with southern Manchuria, whereas accessing Aigun (Heihe) would require either sailing all the way down the Sungari River until its confluence with the Amur and then up the Amur to Heihe, or using a portage over the Lesser Xing'an Mountains between the Nen River valley and the Amur valley. An additional advantage of Qiqihar may have been its location at the junction of a northbound road (to Nenjiang) and a westbound one (to Mongolia), enabling its garrison to defend both against the Russians and the Ölöt Mongols.