What's the meaning of "the Adversary of all Evil" in line 16 of Canto 2 of Inferno by Dante Alighieri, translated by John Ciardi? Here's the context (lines 13–24):
You sang how the father of Sylvius, while still
in corruptible flesh won to that other world,
crossing with mortal sense the immortal sill.
But if the Adversary of all Evil
weighing his consequence and who and what
should issue from him, treated him so well
that cannot seem unfitting to thinking men,
since he was chosen father of Mother Rome
and of her Empire by God’s will and token.
Both, to speak strictly, were founded and foreknown
as the established Seat of Holiness
for the successors of Great Peter’s throne.