Kousséri is a very old city, dating back at least to the Sao civilisation (11th - 16th centuries)2. Its original name is M'sr. Somewhat later called (Qussur: castles) in Arabic. In the 16th century, it was the capital of a Kotoko-language kingdom of M'sr whose elites at least were Islamised, and mentioned in the Italian form Uncusciuri by Giovanni Lorenzo d'Anania. This kingdom was vassal of the kingdom of Kanem-Bornou.
Taken by the army of Rabah Fadlallah (or Rabih Zubaïr) at the end of the 19th century, it was the scene of the battle of Kousséri (22 April 1900), where the French troops of Commander Lamy, allied with the Baguirmians, defeated Rabah. Both chiefs were killed in the course of the battle'.2 The battle of Kousséri favoured the conquest of Chad.
https://fr.wikipedia.org/wiki/Kouséri