For some time it has been thought that the difficulties surrounding the publication date of Callimachus' Aetia and the arrangement of its four books could be resolved by an ingenious theory of Rudolph Pfeiffer. To summarize briefly, the only part of the poem securely datable at the time of Pfeiffer's edition was the last episode of Book 4, the Coma Berenices, which cannot have been composed before 245 b.c. This date may hold for the Prologue as well, where Callimachus refers to himself as an old man. But other parts of the poem seem to have been used by Apollonius of Rhodes and may therefore have been written as early as 270. 1 To account for this discrepancy Pfeiffer posited an early edition of the Aetia that opened with the Somnium, depicting an encounter between Callimachus and the Muses. According to this theory the Somnium served as an introduction both to the entire poem and, more specifically, to the first two books, in the form of a dialogue between the poet and the Muses. This was the version available to Apollonius. Late in life Callimachus decided to reissue his poetry in a collected edition. He then attached a new Prologue and incorporated the Coma Berenices and perhaps other stories as well. Finally, he added an Epilogue (fr.l 12) announcing a transition to the “prosaic pasture of the Muses,” interpreted by Pfeiffer as a reference to the Iambi, which followed in this later edition. 2