Ysengrimus is a Latin fabliau and mock epic, containing a series of anthropomorphic fables thought to have been written in 1148 or 1149 CE by the poet Nivardus.
Florilegia[clarification needed] and medieval catalogs give the author's name variously as "Magister Nivardus", "Balduinus Cecus" (Baldwin the Blind), and "Bernard".
The poem mixes medieval and classical Latin imitations and parts of it are written in a curious, difficult style featuring obscure verb forms such as deponent imperatives.
These stylistic curiosities reflect neither deliberate obscurantism nor lack of poetic talent, rather, they serve as means of characterization.
The poem contains the well-known story in which Reinardus deceives Ysengrimus to go ice fishing using his tail as a net, only to get it frozen into the lake.
Nivardus deals with a subject that received extensive treatment in European popular culture during the Middle Ages and the early modern period.