Friedrich Nietzsche, who in his younger years was one of Wagner's staunchest allies, wrote that, for him, ""Tristan and Isolde" is the real "opus metaphysicum" of all art ... insatiable and sweet craving for the secrets of night and death ... it is overpowering in its simple grandeur". In a letter to his friend Erwin Rohde in October 1868, Nietzsche described his reaction to "Tristan's" prelude: "I simply cannot bring myself to remain critically aloof from this music; every nerve in me is atwitch, and it has been a long time since I had such a lasting sense of ecstasy as with this overture". Even after his break with Wagner, Nietzsche continued to consider "Tristan" a masterpiece: "Even now I am still in search of a work which exercises such a dangerous fascination, such a spine-tingling and blissful infinity as "Tristan" – I have sought in vain, in every art."