Gluck, the German who set himself with real Teutonic zeal and thoroughness to reform French Opera, was a devoted admirer of the old Greek classics. His aim was to give to the operatic stage something of the bigness and dignity of these old giants of art, and posterity has no doubt that he succeeded to a remarkable degree. The libretto of this Opera is founded on Racine's tragedy, which was in some sort an adaptation from Euripides. Agamemnon's daughter Iphigenia was to be offered as a sacrifice to Diana to win for the Greeks a favouring wind to carry them to Troy. The gods, however, intervened, and after Iphigenia had resigned herself to her dread fate, Diana carried her off and a slaughtered hind was seen where she had awaited death.
Racine, listeners will remember, modified the tale to suit the taste of his public. In his play it is Achilles who rescues Iphigenia, and in the libretto of Gluek's opera that ending is followed.
The Overture begins with a mournful tune which is taken from one of Gluck's earlier operas, also on a classical subject. Then there is a still slower interlude, followed by a brisk Allegro in which there are three main tunes, the first two energetic and bold, the third a more smoothly-flowing tune. As Gluck left it, the Overture passes without a break into the opera, but various endings have been made for separate performance. The one most usually played was written by Wagner: it concludes the Overture in the spirit in which the composer would no doubt have done had he meant it to be played separately.

So far as we know, this and one or two similar works of the great Bach owe their origin to the meetings of a University Music Society in Leipzig about the year 1730. Many excellent pianists were available, Bach's own two elder sons among them, and it may be that they took part in performances of this very work. Like a number of Bach's concertos, it is an arrangement, by himself, of one which was originally for another combination, in this case for Violin and Oboe. In its present form it gains greatly in strength and bigness, particularly in the slow Movement, where the modern Pianoforte can sing so much better than the slight instruments for which it was at first composed.
It begins with a vigorous quick movement, in which the two pianofortes and the violins have the first theme together, and the Movement is worked out with all Bach's ingenuity and flow of melody.
In the slow Movement which follows, the second pianoforte begins the tune with very slight accompaniment from the strings, the first following with an imitation of the same tune two bars later.
The last movement, like the first, begins on the violins and two pianofortes in unison, announcing a brisk energetic tune which is the basis of the whole movement.