As indicated in the title, Le Lai de Lanval is a lai. According to the Princeton Encyclopedia of Poetry and Poetics:

In Old French, the oldest narrative lais, almost always written in octosyllables, are [...] short romantic tales originated by Marie de France in the late twelfth century. Most of them have Breton themes, chiefly love but also the supernatural. (p. 780)

In the original French, Marie de France’s lais have eight-syllable lines and rhyming couplets (pairs of rhyming lines). Lais are short narratives compared to more contemporary narrative poetry. Some English translations of the lais attempt to mimic the meter and/or rhyme of the French, but others do not, given how romance languages—like French and Italian—are more suited to rhyming than English.

Arthurian—or chivalric—romances are filled with allusions: references to other notable works. In the Le Lai de Lanval, Marie de France alludes to older Latin and British works. The knights “Gwain” (Line 225) and “Yvain” (Line 226) originally appear in Geoffrey of Monmouth’s History of the Kings of Britain. Marie de France includes them alongside Lanval—a new knight she invents—to place him in the Arthurian canon. Marie de France also alludes to Latin works by Ovid and Tacitus in her inclusion of “Octavian” (Line 85), also known as Caesar Augustus: the wealthy Roman emperor.