English: Lüshun city or Lüshunkou or (literally) Lüshun Port (simplified Chinese: 旅顺口; traditional Chinese: 旅順口; pinyin: Lǚshùnkǒu), formerly known as both Port Arthur and Ryojun, is a town located at the extreme southern tip of the Liaodong Peninsula, in the district of Dalian of the People's Republic of China. It has an excellent natural harbour, the possession and control of which became a casus belli in the Russo-Japanese war (1904–1905). Japanese and then Soviet administration would continue until 1953. During the first decade of that period, it was world famous and was more significant than the other port on the peninsula, today's Dalian. 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 peninsula it was called Ryojun (旅順).