Masked Dispatches: Cryptograms and Cryptology in American History, 1775-1900

Chapter 13. Aaron Burr's "Cipher Letter"

An impulsive adventurer, Aaron Burr, then fifty years old and living in Philadelphia, and still eager to acquire an empire, prepared a secret dispatch that was written in code and cipher and addressed to General James Wilkinson in July 1806. This was the famous letter that would lead President Thomas Jefferson to charge his former vice president and political enemy, Burr, with treason. On the basis of this dispatch, the cunning Wilkinson, who had become a secret, tenured, and well-paid informer ("Agent 13") of the Spanish government in the 1780s, warned Jefferson that a plot, led by Burr and described in the cipher letter, was under way to disrupt the United States and to take over Spain's colony, Mexico. ...