(p.161) Dug in on high ground, Cornwallis had been throwing up earthwork redoubts since early August, employing thousands of slaves who had defected to the British lines in expectation of earning their freedom.
. . .
(p. 164) Cornwallis had grown so desperate that he infected blacks with smallpox and forced them to wander toward enemy lines in an attempt to sicken the opposing forces.
Chernow, Ron. Alexander Hamilton. New York: The Penguin Press, 2004.