I saw this in the Transom. He links to the Catholic Journal
One of the more vivid stories of the Washington Monument is the theft of the Pope’s Stone in 1854, apparently by members of the anti-Catholic, anti-Papist Know-Nothing Party.
It all began with the American nativist movement of the mid-19th century. The nativists sometimes called themselves, ironically enough, Native Americans. They were opposed to the new waves of immigrants, legal or illegal, from countries such as Ireland and Italy. Up until then, most European settlers had been Protestants from such places as Britain and Germany. The newcomers were often Catholic, and grindingly poor besides, such as the Irish fleeing the potato famine.
By the early 1850s these feelings had coalesced into the American party, usually called Know-Nothings. The party acquired the nickname from its “secret” meetings and “hidden” signs, more appropriate to a childrens’ clubhouse than to a political party, and from their habit of answering “I know nothing,” when asked about their activities. The Know-Nothings were very successful for a brief time, especially in the 1856 elections, winning many local and state offices, and even sending members to Congress.
The trouble with the Washington Monument began in 1852, when the February 7 Daily National Intelligencer of Washington, D.C. announced on page 4 the Pope’s intention to contribute a gift tablet, for installation inside the Monument, with the other such tablets on the Monument’s inner walls. The stone came from the Temple of Peace, also rendered as the Temple of Concord, in Rome. The stone was to bear the inscription, in English, of “Rome to America.”
Here's the rest