Although Arrigo Boito devoted 56 years to the composition of his Nerone, at his death the opera was still incomplete; Arturo Toscanini bustled to refine and finish the last act for the work’s premiere at La Scala on 1 May 1924.
Since the figure of the mad psychopath Nero is best remembered in the collective imagination as he plays and sings while observing the Great Fire of Rome, for the first staging of the opera a true kithara was made by the lute maker Piero Parravicini at the Milan workshop of Antonio Monzino e Figli; today the instrument is on display at the Civico Museo degli Strumenti Musicali in Milan.
This according to “‘Or che i Numi son vinti, a me la cetra, a me l’altar!’: Kithara constructed for the premiere of Arrigo Boito’s Nerone” by Donatella Melini (Music in art XL/1–2  pp. 267–72).
Above, the instrument in question (click to enlarge); below, the scene referred to in the article’s title.