Ezio is an opera seria from the Early Classical Period in three acts composed by Christoph Willibald Gluck, staged in 1750 and revised in 1763.
Unlike the two completely different settings of the text by Mysliveček, Naples (1775) and Munich (1777), Gluck's two versions share about half their music.
Gluck, as Handel and Vivaldi before him and all composers of his time, naturally recycled the "numbers" (arias and choruses) from older operas, rewriting the connecting recitative as necessary.
In 1763 he reused nearly half of the 25 musical numbers from the Prague Ezio of 13 years earlier, avoiding material like "Se povero il ruscello" from the Prague Ezio which he had already used at the Vienna Burgtheater the previous year in the Vienna Orfeo as "Che puro ciel," and Gluck filled up the rest with 7 arias from Il trionfo di Clelia, which was also unknown to Viennese audiences.
Recycling the arias from the Prague Ezio and Il trionfo di Clelia still required Gluck to transpose and adjust for the new singers, and reorchestrate for a bigger orchestra.