 Guibert of Gembloux was invited to finish the work; however, he had to return to his monastery with the project unfinished.Theoderic utilized sources Guibert had left behind to complete the "Vita".Hildegard's works include three great volumes of visionary theology; a variety of musical compositions for use in liturgy, as well as the musical morality play "Ordo Virtutum"; one of the largest bodies of letters (nearly 400) to survive from the Middle Ages, addressed to correspondents ranging from popes to emperors to abbots and abbesses, and including records of many of the sermons she preached in the 1160s and 1170s; two volumes of material on natural medicine and cures; an invented language called the "Lingua ignota" ("unknown language"); and various minor works, including a gospel commentary and two works of hagiography.