Heihe (Chinese: 黑河; pinyin: Hēihé; lit. 'Black River'; 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. Heihe, formerly Aihui or Aigun, is one of the five oldest cities in Heilongjiang, along with Qiqihar, Yilan, Acheng and Hulan. Human beings started to settle in Heihe region as early as the Paleolithic Age.[2] 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.[2] It was established some 30 km (19 mi) south of the modern city site[3] (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).