 This was a collection of already published poems.No one expected it would be one of the most popular books of German verse ever published and sales were slow to start with, picking up when composers began setting Heine's poems as Lieder.For example, the poem "Allnächtlich im Traume" of the "Buch der Lieder" was set to music by Robert Schumann as well as by Felix Mendelssohn.