Irenaeus on 666 and 616
Irenaeus of Lyons In his Against Heresies, Irenaeus argues that 666 is a particularly “fitting” number for the name of the beast in Rev 13:18: since he sums up in his own person all the commixture of wickedness which took place previous to the deluge, due to the apostasy of the angels. For Noah was six hundred years old when the deluge came upon the earth, sweeping away the rebellious world, for the sake of that most infamous generation which lived in the times of Noah. And [Antichrist] also sums up every error of devised idols since the flood, together with the slaying of the prophets and the cutting off of the just {cf. Matt 24:37–38/ Luke 17:26–27}. For that image which was set up by Nebuchadnezzar had indeed a height of sixty cubits, while the breadth was six cubits; on account of which Ananias, Azarias, and Misaël, when they did not worship it, were cast into a furnace of fire, pointing out prophetically, by what happened to them, the wrath against the righteous which shall arise towards the [time of the] end {cf. Matt 24:15/ Mark 13:14}. For that image, taken as a whole, was a prefiguring of this man’s coming, decreeing that he should undoubtedly himself alone be worshipped by all men {cf. Rev 13:15}. Thus, then, the six hundred years of Noah, in whose time the deluge occurred because of the apostasy, and the number of the cubits of the image for which these just men were sent into the fiery furnace, do indicate the number of the name of that man in whom is concentrated the whole apostasy of six thousand years, and unrighteousness, and wickedness, and false prophecy, and deception; for which things’ sake a cataclysm of fire shall also come [upon the earth]. (Irenaeus, Against Heresies, 5.29.2 [ ANF 1:558; affiliate disclosure] square brackets original; curled brackets added) ...