In August of 1819 Shelley completed _The Cenci_.

During its progress he had talked over with Mary the arrangement of scenes; he had even suggested at the outset that she write the tragedy herself.
And about a year earlier he had been urging upon her a translation of Alfieri's _Myrrha_.

Thomas Medwin, indeed, thought that the story which she was writing in 1819 was specifically based on _Myrrha_.

That she was thinking of that tragedy while writing _Mathilda_ is evident from her effective use of it at one of the crises in the tale.

And perhaps she was remembering her own handling of the theme when she wrote the biographical sketch of Alfieri for Lardner's _Cabinet Cyclopaedia_ nearly twenty years later.