Did you also know that the Latin form of "vicar of Christ" adds up to 666 if you count the letters in it that are also Roman Numerals? Try it. The Latin is

VICARIVS FILII DEI (literally, In the place of the Son of God)

V=5
I=1
C=100
I=1
V=5
I=1
L=50
I=1
I=1
D=500
I=1
________
666

I've heard that this Latin title for the Antichrist is carved on the Pope's throne or ceremonial chair or whatever it is, or the alternative story that it's on his fish-head shaped hat or mitre. Maybe it's on both.