Montdidier (French pronunciation: [mɔ̃didje]; Picard: Montdidji or Mondidji) is a commune in the Somme department in the administrative region of Hauts-de-France (historically Picardy), northern France.

[5] Under Charlemagne, a donjon was built in the north-west of the town, on a chalk promontory, (nowadays the site of the Prieuré).

It was here, in 774, that Desiderius, king of the Lombards, was held prisoner by Charlemagne, giving the town its name (in French, Didier).

Around the year 948, the first church was built near the castle by Heldwide, the wife of Hilduin, first of the house of the Counts of Montdidier.

[6] In 1184, King Philip II of France had the outlying buildings of the town burnt down,[7] during the war for the possession of the Amiénois and the Vermandois.