Tancredi is a melodramma eroico (opera seria or 'heroic' opera) in two acts by composer Gioachino Rossini and librettist Gaetano Rossi (who was also to write Semiramide ten years later), based on Voltaire's play Tancrède (1760). The opera made its first appearance at the Teatro La Fenice in Venice on 6 February 1813, and because Il signor Bruschino premiered in late January, the composer must have completed Tancredi in less than a month. The overture, borrowed from La pietra del paragone, is a popular example of Rossini's characteristic style and is regularly performed in concert and recorded.
Considered by Stendhal, Rossini's earliest biographer, to be "high amongst the composer's masterworks", and describing it as "a genuine thunderbolt out of a clear, blue sky for the Italian lyric theatre," his librettist Gaetano Rossi notes that, with it, "Rossini rose to glory". Richard Osborne proclaims it to be "his fully fledged opera seria and it established him, more of less instantly, as Italy's leading composer of contemporary opera."
Although the original version had a happy ending (as required by the opera seria tradition), soon after the Venice premiere, Rossini—who was more of a Neo-classicist than a Romantic, notes Servadio—had the poet Luigi Lechi rework the libretto to emulate the original tragic ending by Voltaire. In this new ending, presented at the Teatro Comunale in Ferrara on 21 March 1813, Tancredi wins the battle but is mortally wounded, and only then does he learn that Amenaide never betrayed him. Argirio marries the lovers in time for Tancredi to die in his wife's arms.
As has been stated by Philip Gossett and Patricia Brauner, it was the rediscovery of the score of this ending in 1974 (although elsewhere Gossett provides evidence that it was 1976) that resulted in the version which is usually performed today.