The premiere of Fidelio, at the Theater an der Wien on the evening of November 20, 1805, took place only seven days after Napoleon's army had entered Vienna. Members of the Austrian nobility, who typically supported Beethoven, had fled the city, which means that not many people attended the first performance. Poor attendance and unfavorable reviews led to the withdrawal of the opera after only three performances. Beethoven's subsequent revision, combining the first two acts into one (resulting in a two-act format), premiered on March 29, 1806, but there was only one performance. However, Napoleon's subsequent losses throughout Europe in 1812-1814 emboldened the Viennese, and in this atmosphere of triumph the Kärntnertor-Theater in Vienna requested a revival of the opera. Beethoven made numerous changes to the score and composed a new overture. Beethoven's third version of Fidelio was first performed May 23, 1814; however, the overture would not be heard until the second performance on May 26. This overture, the fourth that Beethoven composed for the opera, has remained as the standard overture since its composition. The Leonore Overture No. 2, performed for the first version of the opera, is a successful curtain raiser, but its anticipation of the climax of the second act proved destructive to the drama. Leonore Overture No. 3 is a revision of No. 2, while the overture Leonore No. 1, Op. 138, was found among Beethoven's papers after his death; it is not linked to either of the first two productions, and may have been written for a projected Prague performance of 1807. Unlike Leonore Overtures 2 and 3, this work does not anticipate the music of the drama.
Cast in sonata form, it opens with a fortissimo outburst that is a fragment of the first theme. This gives way to the main theme, played by the horn, a moment later. The secondary theme, for a combination of horn and strings, is even more forceful than the first, and the exposition moves to the development without repeat. Brief and intense, the development section almost imperceptibly becomes the recapitulation, and the return of the opening measures marks the beginning of a triumphant coda. The choice of E major for the overture of an opera in C major may seem curious, especially when all three Leonore overtures are in C major. But E major is a bright key, anticipating the liberation of Florestan without actually quoting the music, and it is the same key as Leonore's aria, "Komm, Hoffnung" ("Come, hope").