As the Allies began a careful reconnaissance of the British fortifications on 28 and 29 September, British General Cornwallis cautiously withdrew his men from the outermost works to his main defensive line on 30 September 1781. He was concerned that these isolated outposts would simply be surrounded and cut off if they remained where they were.
“We find ourselves very unexpectedly upon very advantageous ground,” wrote Jonathan Trumbull, Washington’s aide, on 30 September. “At night our troops begin to throw up some works and to take advantage of the enemy’s evacuated labors.” For besieging troops, the abandoned redoubts gave them a covered and concealed position from which to begin the laborious task of digging the trenches to protect laborers building covered positions for the artillery. Everything in a siege revolved around acquiring superior positions for artillery where they could fire at vulnerable positions in the enemy lines while not being exposed to the massed fire of the enemy’s batteries.
Philbrick, In the Hurricane’s Eye
Colonial Williamsburg