The closing ceremony of the Second Vatican Council in St. Peter Square on Dec. 9, 1965. Forty bishops pledged to forsake worldly goods, but the agreement was largely ignored. Pope Francis' emphasis on helping the poor has revived talk about the Pact of the Catacombs. Keystone-France/Gamma-Keystone via Getty Images hide caption

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Army soldiers and police patrol a street in the center of Brussels on Wednesday. Students are returning to class after a shutdown over fears that a series of simultaneous attacks could be launched around the Belgian capital. Geert Vanden Wijngaert/AP hide caption

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Paris Prosecutor Francois Molins delivers a press conference Tuesday about the Nov. 13 attacks that claimed 130 lives in the French capital. Loic Venance/AFP/Getty Images hide caption

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