Siface re di Numidia (also: Siface or Viriate) is a libretto in three acts by Pietro Metastasio. It is a reworking of La forza della virtù by de:Domenico David and was Metastasio's first work as a librettist. it was first performed with a setting to music by Francesco Feo on 13 May 1723 at the Teatro San Bartolomeo, Naples.