That you be not easily moved from your sense, nor be terrified, neither by spirit, nor by word, nor by epistle, as sent from us, as if the day of the Lord were at hand.  Let no man deceive you by any means, for unless there come a revolt first, and the man of sin be revealed, the son of perdition,  Who opposeth, and is lifted up above all that is called God, or that is worshipped, so that he sitteth in the temple of God, shewing himself as if he were God.
-- Second Epistle Of Saint Paul To The Thessalonians 2:2-4
5. When all this is considered there is good reason to fear lest this great perversity may be as it were a foretaste, and perhaps the beginning of those evils which are reserved for the last days; and that there may be already in the world the "Son of Perdition" of whom the Apostle speaks (II. Thess. ii., 3). Such, in truth, is the audacity and the wrath employed everywhere in persecuting religion, in combating the dogmas of the faith, in brazen effort to uproot and destroy all relations between man and the Divinity! While, on the other hand, and this according to the same apostle is the distinguishing mark of Antichrist, man has with infinite temerity put himself in the place of God, raising himself above all that is called God; in such wise that although he cannot utterly extinguish in himself all knowledge of God, he has contemned God's majesty and, as it were, made of the universe a temple wherein he himself is to be adored. "He sitteth in the temple of God, showing himself as if he were God" (II. Thess. ii., 2).
-- From "E SUPREMI" ENCYCLICAL OF POPE PIUS X ON THE RESTORATION OF ALL THINGS IN CHRIST. OCTOBER 4, 1903