 The theme of the "Berceuse" echos a song that Chopin may have heard in his childhood, "Już miesiąć zeszedł, psy się uśpily" (The moon now has risen, the dogs are asleep).Chopin completed "Berceuse" in 1844, shortly before his Piano Sonata in B minor.It is a series of 16 variations on an ostinato ground bass.