The evolution of Richard Wagner's operatic tetralogy Der Ring des Nibelungen (The Ring of the Nibelung) was a long and tortuous process, and the precise sequence of events which led the composer to embark upon such a vast undertaking is still unclear. The composition of the text took place between 1848 and 1853, when all four libretti were privately printed; but the closing scene of the final opera, Götterdämmerung, was revised a number of times between 1856 and 1872. The names of the last two Ring operas, Siegfried and Götterdämmerung, were probably not definitively settled until 1856.