Revelation 13: 18: Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.
“Vicarivs Filii Dei” means in Latin, “Vicar of the Son of God,” and is the title attributed to the Pope. Certain letters of the Latin alphabet are also used as numbers, and when those letters incorporated within the popish title are added together, they equate to 666.
V (5 in Latin) + I (1 in Latin) + C (100 in Latin) + I (1) + V (5) + I (1) + L (50 in Latin) + I (1) + I (1) + D (500 in Latin) + I (1) = 666