Saint Augustine of Hippo
There is a false quote going around the internet that claims Saint Augustine, Father and Doctor of the Church, called for the massacre of Jews. This is the following quote.
“How hateful to me are the enemies of your Scripture! How I wish that you would slay them (the Jews) with your two-edged sword, so that there should be none to oppose your word! Gladly would I have them die to themselves and live to you!” (Confessions 12:14)
This is misquoted, perhaps intentionally, to discredit Saint Augustine who is very important in Church history. Here is the accurate quote.
“Wonderful is the depth of Your oracles, whose surface is before us, inviting the little ones; and yet wonderful is the depth, O my God, wonderful is the depth. It is awe to look into it; and awe of honour, and a tremor of love. The enemies thereof I hate vehemently. Oh, if You would slay them with Your two-edged sword, that they be not its enemies! For thus do I love, that they should be slain unto themselves that they may live unto You.”
Note that the two-edged sword is a reference to the word of God (rf. Ephesians 6:17, Hebrew 4:12), and that this same two-edged sword is “the sword of the Spirit”. Also note how the passage does not make mention of the Jews at all specifically. This is a passage in reference to any group which rejects the Lord Jesus Christ, hence “are the enemies of [God’s] Scripture”. So, for the slaying part this is more like a slaying in the Spirit, a conversion to Christendom, but not a call to physical violence. The purpose of this slaying was “that they be not [the Gospel’s] enemies”, and “that they may live unto” God.
The pilleus cornutus, a hat Jews had to wear whilst outside of ghettos
In fact, Saint Augustine defended the existence of the Jews saying, “Slay not them of whom the sins Thou slayest” . Perhaps, he sees the existence of Judaism to be a necessary evil in saying, “Let the nation of the Jews remain: . . . In order that He may show to us among our enemies His mercy” . Thomas Madden even acknowledges that Saint Augustine “was quick to insist that the faithful not engage in wars of religious conversion or for the purpose of destroying heresies or pagans” .
 Saint Augustine of Hippo. Exposition on Psalm 59, no. 18. <http://www.newadvent.org/fathers/1801059.htm>.
 Madden, Thomas F. New Concise History of the Crusades. Lanham: Rowman & Littlefield Publishers, Inc. 2006. Print. p. 2.