In most of Wagner's music dramas the source material, generally deep-rooted in Germanic or Celtic tradition, is well known, and Wagner's ndebtedness is transparent. The four works composing Der Ring des Nibelungen, for example, are based chiefly on the Volsunga saga and the Nibelungenlied. Similarly, Wolfram von Eschenbach's Parzival was the inspiration for Wagner's Parsifal, and the Tristan of Gottfried von Strassburg was followed closely in Tristan und Isolde. These mediaeval works are epic monuments of western European legend or chefs d‘œuvre of the Minnesingers’ art. Wagner has thus ambitiously concerned himself with subjects of impressive grandeur, drawn from sources of no inconsiderable importance.