Old Spanish, also known as Old Castilian (Spanish: castellano antiguo; Old Spanish: roman [roˈman], romançe, romaz), or Medieval Spanish (Spanish: español medieval), was originally a dialect of Vulgar Latin spoken in the former provinces of the Roman Empire that provided the root for the early form of the Spanish language that was spoken on the Iberian Peninsula from the 10th century until roughly the beginning of the 15th century, before a series of consonant shifts gave rise to modern Spanish. The poem Cantar de Mio Cid ('The Poem of the Cid'), published around 1200, is the best known and most extensive work of literature in Old Spanish. Source: Wikipedia (en)