The earliest French literature dates from the Middle Ages, when what is now known as modern France did not have a single, uniform language. There were several languages and dialects, and writers used their own spelling and grammar. Some authors of French medieval texts are unknown, such as ''Tristan and Iseult'' and ''Lancelot-Grail''. Other authors are known, for example Chrétien de Troyes and Duke William IX of Aquitaine, who wrote in Occitan.