Lüshunkou District (also Lyushunkou District; simplified Chinese: 旅顺口区; traditional Chinese: 旅順口區; pinyin: Lǚshùnkǒu Qū) is a district of Dalian, in Liaoning province, China. Also formerly called Lüshun City (旅顺市; 旅順市; Lǚshùn Shì) or literally Lüshun Port (旅顺港; 旅順港; Lǚshùn Gǎng), it was formerly known as both Port Arthur (亚瑟港; 亞瑟港; Yàsè Gǎng; Russian: Порт-Артур, romanized: Port-Artur) and Ryojun (Japanese: 旅順). The district's area is 512.15 square kilometres (197.74 sq mi) and its permanent population as of 2010 is 324,773.
Lüshunkou is located at the extreme southern tip of the Liaodong Peninsula. It has an excellent natural harbor, the possession and control of which became a casus belli of the Russo-Japanese War (1904–05). Japanese and then Russian administration was established in 1895 and continued until 1905 when control was ceded to Japan. During the first decade of that period, it was world-famous and was more significant than the other port on the peninsula, Dalian proper. In Western diplomatic, news, and historical writings, it was known as Port Arthur, and during the period when the Japanese controlled and administered the Liaodong (formerly Liaotung) Peninsula it was called Ryojun (旅順), the Japanese pronunciation of the Chinese characters in the city's name. After the Japanese defeat in World War II, the city was under the administration of the Soviet Union, which rented the port from China, until 1950. Although the Russians presented the port to China in 1950, Soviet troops remained in the city until 1955.
Central Dalian is some 64 kilometres (40 miles) farther up the coast, sprawling around the narrowest neck of the Liaodong Peninsula (simplified Chinese: 辽东半岛; traditional Chinese: 遼東半島; pinyin: Liáodōng Bàndǎo), whereas Lüshun occupies its southern tip. (See Landsat Map below Zoomed – Lüshun City surrounds the lake-like structure clearly visible near the peninsular tip—the lake-like feature is the inner natural harbour of the port, a very well-sheltered and fortifiable harbour to 19th century eyes.)