it is my understanding that 666 is another of those things that was hijacked
by early christianity. 999 an old Pagan symbol for life was inverted and made the "sign of the beast."
REVELATION 13:1-18
And I stood upon the sand of the sea, and saw a beast rise up out of the sea, having seven heads and ten horns, and upon his horns ten crowns, and upon his heads the name of blasphemy.
2 And the beast which I saw was like unto a leopard, and his feet were as the feet of a bear, and his mouth as the mouth of a lion: and the dragon gave him his power, and his seat, and his great authority.
3 And I saw one of his heads as it were wounded to death; and his deadly wound was healed: and all the world wondered after the beast.
4 And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
8 And all that dwell upon the earth shall worship him, whose names are not written in the book of the Lamb slain from the foundation of the world.
9 If any man have an ear, let him hear.
10 He that leadeth into captivity, shall go into captivity: he that killeth with the sword, must be killed with the sword. Here is the patience and the faith of the saints.
11 And I beheld another beast coming up out of the earth, and he had two horns like a lamb, and he spaketh as a dragon.
16 And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads;
17 And that no man might buy or sell, save he that has the mark, or the name of the beast, or the number of his name.
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.
Rev 13:14 And because of the signs (miracles) which he is allowed to perform in the presence of the [first] beast, he deceives those who inhabit the earth, commanding them to erect a statue (an image) in the likeness of the beast who was wounded by the [small] sword and still lived. [Deut. 13:1-5.]
Rev 13:15 And he is permitted [also] to impart the breath of life into the beast's image, so that the statue of the beast could actually talk and cause to be put to death those who would not bow down and worship the image of the beast. [Dan. 3:5.]
Rev 13:16 Also he compels all [alike], both small and great, both the rich and the poor, both free and slave, to be marked with an inscription [stamped] on their right hands or on their foreheads,
Rev 13:17 So that no one will have power to buy or sell unless he bears the stamp (mark, inscription), [that is] the name of the beast or the number of his name.
Rev 13:18 Here is [room for] discernment [a call for the wisdom of interpretation]. Let anyone who has intelligence (penetration and insight enough) calculate the number of the beast, for it is a human number [the number of a certain man]; his number is 666.
www.usccb.org...
[18] Each of the letters of the alphabet in Hebrew as well as in Greek has a numerical value. Many possible combinations of letters will add up to 666, and many candidates have been nominated for this infamous number. The most likely is the emperor Caesar Nero (see the note on Rev 13:3), the Greek form of whose name in Hebrew letters gives the required sum. (The Latin form of this name equals 616, which is the reading of a few manuscripts.) Nero personifies the emperors who viciously persecuted the church. It has also been observed that "6" represents imperfection, falling short of the perfect number "7," and is represented here in a triple or superlative form.