Heihe (; ; Russian: Хэйхэ) is a prefecture-level city of northern Heilongjiang province, China, located on the Russian border, on the south bank of the Amur (Heilong) River, across the river from Blagoveshchensk. At the 2020 census, 1,286,401 people lived in the prefecture-level city of whom 223,832 lived in the built-up area (or metro) made of Aihui District. Heihe marks the northeast terminus of the diagonal Heihe–Tengchong Line, which is sometimes used to divide China into east and west. History Heihe, formerly Aihui or Aigun, is one of the five oldest cities in Heilongjiang, along with Tsitsihar, Yilan, Acheng and Hulan. Human beings started to settle in Heihe region as early as the Paleolithic Age. Later it became home to local tribes. During the Qing dynasty, Heihe was the first place troops sent to Heilongjiang were stationed. The predecessor of today's Heihe was the town established by the indigenous Ducher people of the Amur Valley in the mid-1650s. It was established some south of the modern city site (in today's Aihui District) and was known as Aigun, Heilongjiang, or Saghalien Ula. (The two last names both mean "the Black Dragon River" - the name for the Amur River in Chinese and Manchu, respectively). After the Ducher were evacuated by the Qing to the Sungari or Hurka in the 1650s, the Ducher town was probably vacated. However, in 1683-85 the Manchus re-used the site as a base for their campaign against the Russian fort of Albazin. Aigun was the capital (the seat of the military governor) of Heilongjiang from 1683 to 1690, before the capital was moved to Nenjiang (Mergen). After the capture of Albazin in 1685 or 1686, the Qing governor relocated the town to a new site on the right (southwestern) bank of the Amur, about 3 miles downstream from the original. The new site occupied the location of the former village of the Daurian chief named Tolga. The city became known primarily under its Manchu name Saghalien Ula hoton (Manchu: sahaliyan ula hoton) and Chinese name Heilongjiang Cheng (), which both mean "Black River City". Later the governor office was transferred to Qiqihar. However, Aigun remained the seat of the Deputy Lieutenant-General (Fu dutong), responsible for a large district covering much of the Amur Valley within the province of Heilongjiang as it existed in those days. Aigun was visited around 1709 as a part of a nationwide Sino-French