[Composed at Este, September, October, 1818 (Act 1); at Rome, March-April 6, 1819 (Acts 2, 3); at Florence, close of 1819 (Act 4). Published by C. and J. Ollier, London, summer of 1820. Sources of the text are (1) edition of 1820; (2) text in "Poetical Works", 1839, prepared with the aid of a list of errata in (1) written out by Shelley; (3) a fair draft in Shelley's autograph, now in the Bodleian. This has been carefully collated by Mr. C.D. Locock, who prints the result in his "Examination of the Shelley Manuscripts in the Bodleian Library", Oxford (Clarendon Press), 1903. Our text is that of 1820, modified by edition 1839, and by the Bodleian fair copy. In the following notes B = the Bodleian manuscript; 1820 = the editio princeps, printed by Marchant for C. and J. Ollier, London; and 1839 = the text as edited by Mrs. Shelley in the "Poetical Works", 1st and 2nd editions, 1839. The reader should consult the notes on the Play at the end of the volume.] PREFACE. The Greek tragic writers, in selecting as their subject any portion of their national history or mythology, employed in their treatment of it a certain arbitrary discretion. They by no means conceived themselves bound to adhere to the common interpretation or to imitate in story as in title their rivals and predecessors. Such a system would have amounted to a resignation of those claims to preference over their competitors which incited the composition. The Agamemnonian story was exhibited on the Athenian theatre with as many variations as dramas.