In 'Iphigénie en Tauride,' the last of his great works, which was produced in 1778, Gluck reached his highest point. Here he seems for the first time thoroughly to fuse and combine the two elements which are for ever at war in his earlier operas, musical beauty and dramatic truth. Throughout the score of 'Iphigénie en Tauride' the declamation is as vivid and true as in 'Alceste,' while the intrinsic loveliness of the music yields not a jot to the passion-charged strains of 'Armide.' The overture paints the gradual awakening of a tempest, and when the storm is at its height the curtain rises upon the temple of Diana at Tauris, where Iphigenia, snatched by the goddess from the knife of the executioner at Aulis, has been placed as high priestess. The priestesses in chorus beseech the gods to be propitious, and when the fury of the storm is allayed, Iphigenia recounts her dream of Agamemnon's death, and laments the woes of her house. She calls upon Diana to put an end to her life, which already has lasted too long. Thoas, the king of the country, now enters, alarmed by the outcries of the priestesses. He is a prey to superstitious fears, and willingly listens to the advice of his followers, that the gods can only be appeased by human blood. A message is now brought that two young strangers have been cast upon the rock-bound coast, and Thoas at once decides that they shall be the victims. Orestes and Pylades are now brought in. They refuse to make themselves known, and are bidden to prepare for death, while the act closes with the savage delight of the Scythians.
The second act is in the prison. Orestes bewails his destiny, and refuses the consolation which Pylades offers in a noble and famous song. Pylades is torn from his friend's arms by the officers of the guard, and Orestes, left to himself, after a paroxysm of madness sinks to sleep upon the prison floor. His eyes are closed, but his brain is a prey to frightful visions. The Furies surround him with horrible cries and menaces, singing a chorus of indescribable weirdness. Lastly, the shade of the murdered Clytemnestra passes before him, and he awakes with a shriek to find his cell empty save for the mournful form of Iphigenia, who has come to question the stranger as to his origin and the purpose of his visit to Tauris. In broken accents he tells her—what is new to her ears—the tale of the murder of Agamemnon, and the vengeance taken upon Clytemnestra by himself; adding, in order to conceal his own identity, that Orestes is also dead, and that Electra is the sole remnant of the house of Atreus. Iphigenia bursts into a passionate lament, and the act ends with her offering a solemn libation to the shade of her brother.
In the third act Iphigenia resolves to free one of the victims, and to send him with a message to Electra. A sentiment which she cannot explain bids her choose Orestes, but the latter refuses to save his life at the expense of that of his friend. A contention arises between the two, which is only decided by Orestes swearing to take his own life if Pylades is sacrificed. The precious scroll is thereupon entrusted to Pylades, who departs, vowing to return and save his friend.
In the fourth act Iphigenia is a prey to conflicting emotions. A mysterious sympathy forbids her to slay the prisoner, yet she tries to steel her heart for the performance of her terrible task, and calls upon Diana to aid her. Orestes is brought on by the priestesses, and while urging Iphigenia to deal the blow, blesses her for the pity which stays her hand. Just as the knife is about to descend, the dying words of Orestes, 'Was it thus thou didst perish in Aulis, Iphigenia my sister?' bring about the inevitable recognition, and the brother and sister rush into each other's arms. But Thoas has yet to be reckoned with. He is furious at the interruption of the sacrifice, and is about to execute summary vengeance upon both Iphigenia and Orestes, when Pylades returns with an army of Greek youths—whence he obtained them is not explained—and despatches the tyrant in the nick of time. The opera ends with the appearance of Pallas Athene, the patroness of Argos, who bids Orestes and his sister return to Greece, carrying with them the image of Diana, too long disgraced by the barbarous rites of the Scythians.
'Echo et Narcisse,' an opera cast in a somewhat lighter mould, which was produced in 1779, seems to have failed to please, and 'Iphigénie en Tauride' may be safely taken as the climax of Gluck's career. It is the happiest example of his peculiar power, and shows more convincingly than any of its predecessors where the secret of his greatness really lay. He was the first composer who treated an opera as an integral whole. He was inferior to many of his predecessors, notably to Handel, in musical science, and even in power of characterisation. But while their works were often hardly more than strings of detached scenes from which the airs might often be dissociated without much loss of effect, his operas were constructed upon a principle of dramatic unity which forbade one link to be taken from the chain without injuring the continuity of the whole. In purely technical matters, too, his reforms were far-reaching and important. He was first to make the overture in some sort a reflection of the drama which it preceded, and he used orchestral effects as a means of expressing the passion of his characters in a way that had not been dreamed of before. He dismissed the harpsichord from the orchestra, and strengthened his band with clarinets, an instrument unknown to Handel. His banishment of recitativo secco, and his restoration of the chorus to its proper place in the drama, were innovations of vast importance to the history of opera, but the chief strength of the influence which he exerted upon subsequent music lay in his power of suffusing each of his operas in an atmosphere special to itself.