An insertion aria (also known as interpolated aria, trunk aria, or aria di baule in Italian) is an aria sung in an opera for which it was not composed. It was a practice that began in the seventeenth century and continued actively through the late 19th century and sporadically through the 20th century. The insertion aria could replace an existing aria, or might be added to an opera. All insertions were planned in advance. They might be composed by the same composer of the opera, or might have been written by a different composer, with or without the knowledge of the opera's composer. Most insertions were of arias; infrequently non-operatic songs were inserted. Insertions could consist of arias, duets, ensembles, even entire scenes. Although men and women singers used insertion, women are t