"Possente spirto, e formidabil nume" ("Mighty spirit and formidable god") is a key aria[1] from Act 3 of Claudio Monteverdi's opera L'Orfeo, where Orpheus attempts to persuade Charon to allow him to pass into Hades and find Euridice.
Orpheus crosses over the Styx in Charon's boat, singing Rendetemi il mio ben, tartarei Numi!
The Chorus of Spirits then sing Nulla impresa per uom si tenta invano, (No enterprise of man is undertaken in vain...) to close the third act.
This aria is one of the most important musical documents of early Italian Baroque performance practice.
In the original published edition (1607), Monteverdi uniquely includes two separate versions for Orfeo to sing, one simple and one elaborately ornamented.