http://www.villagehistorian.org/Documents/EncampmentAlliedArmies15slides0001.pdf "The Washington-Rochambeau Encampment of the American and French Armies at Dobbs Ferry, Ardsley, Hartsdale and Edgemont"] A large British army controlled Manhattan at the time, and Washington chose the Dobbs Ferry area for encampment because he hoped to probe for weaknesses in the British defenses, just 12 miles to the south.