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boatload of Napoleonic exiles sailed from Philadelphia on Dec. 18, 1817 on a mysterious mission to establish a secret sanctuary for their imprisoned hero in Spanish Texas.

Since he always preferred to keep power in the family, Napoleon Bonaparte put no fewer than four siblings on as many European thrones. His oldest brother Joseph ruled Spain for five years before fleeing with 50 million francs to, of all places, New Jersey.

In the aftermath of the disaster at Waterloo in 1815, the Little Corpor...