On September 28, when the allies left Williamsburg headed for Yorktown there were some 8,845 Americans under command of General Washington. Of those almost 40 percent were made up of Virginia Militia and under the command of Virginia governor, Brigadier General Thomas Nelson, Jr. who was also a resident of Yorktown. The French wing, commanded by Lieutenant General de Rochambeau totaled about 7,800. Behind the fortifications that Cornwallis had erected during the previous month were about 6,000. On September 24th, Cornwallis received a dispatch from Clinton telling him that he was dispatching some 5,000 additional troops that should be arriving at Yorktown in a few days, which would bring Cornwallis' forces to about 11,000 well-trained men.
Although the allies did encounter some light infantry pickets on the British right, they departed during the first night. The allies formed a camp that extended from above the town in a large arc about 6 miles long extending from the York River around to Wormley Creek below the town.
The British had erected in a curve, a long series of redoubts (7) and entrenchments. Further out was another series of earthen walls and 3 smaller redoubts on the west side of town and 2 redoubts on the east.
During the night the allies had begun building their entrenchments and fortifications surprising the British on the morning of the 29th. The allies continued building their walls throughout the day. On the morning of the 30th, the allies discovered that the English had surprisingly abandoned their outer entrenchments except for the a couple of redoubts. Cornwallis would later be criticized for giving up those outer entrenchments without a fight. The reason he gave was that Clinton's promise of 5,000 reinforcements would arrive in a few days. Cornwallis decided with that information, to concentrate his forces inside the inner defenses rather than risk losing his artillery pieces during an early engagement.
Cornwallis' inner works were enclosed unlike the outer works which were singular positions that could have been easily overtaken during a mass assault. Cornwallis felt with the size of his opponents, and his relatively weak position, it would be better not to waste his manpower and munitions in indefensible positions.
During the first week of October allies continued to prepare for the upcoming siege. During this time 1200 Americans were sent into the woods to gather sticks and vines to make baskets that would be used in building the outer defensive walls from which they could install a variety of artillery pieces that could used in bombarding British positions.
The 1000s of baskets required would be filled with dirt and stacked one upon another so the walls could be constructed in such a way as to absorb an incoming cannonball and still be high enough to protect the soldiers on the opposite side. These walls were built along the road leading up from the James River and would be used to protect the men and animals from British fire as they manually carried the heavy siege guns up from the river and put into position. By October 6, all was ready for the siege to begin. The heavy guns were in position and ready to fire.
Once the defensive positions were completed, digging a parallel trench was begun at about 600 yards from the British lines by some 1500 men digging while 2800 men guarded them. They worked throughout the night and by morning, they had a trench deep enough to conceal their work from enemy fire. By the 9th, there were enough artillery positions setup to begin firing against the British positions.
On the 10th of October more artillery positions came online. British ships anchored in the river also came under fire. One ship, the Charon was set afire from artillery shells. It burned down to the water line and drifted across the river where it sank.
Meanwhile, digging continued along the parallel. To help protect the digging operation 4 redoubts were built and 5 batteries were erected along the parallel to help protect the diggers from attacks by British sorties. Besides this backbreaking work, illness had become a major problem along the lines on both sides. Over 1,000 on the American side were reporting debilitating illness. It was the same on the British side.
During the night of the 11th, 750 yards of the new parallel were completed. The trench was more than 3 foot deep and 7 foot wide with dirt piled on the enemy side to increase the protection. American forces were nearing the left flank of the British line enforced by 2 reinforced positions called redoubts. The goal of the digging was to approach these redoubts, bringing the trench to within striking distance.
The French forces took up position on the left side of the town and above the Beaverdam Creek. The Americans took up position to the right and below the creek.
During the day of September 29, the American and French forces began digging a series of trenches and earthen walls where they would position their artillery pieces. During the night, the British had quietly abandoned their outer defensive positions. As soon as this withdrawal became known, the colonial forces moved forward and occupied the enclosures, quickly reworking them so their artillery would be facing Yorktown.
By September 9, French artillery began firing against the British. With the American battery set to begin, George Washington was given the honor of firing the first round. From that moment until the British flag of truce was waived some X days later, some 1700 artillery shells would be fired each day by both French and American batteries.
Only two things stood in the way of the final assault on Cornwallis: two redoubts on his left flank. Redoubts were a common component of European warfare. They were entirely enclosed fortifications large enough of being defended by a 100 or more men. These two fortifications were placed southeast of the town and helped protect the town from infantry attacking along the river. The two redoubts posed a serious obstacle that had to be taken.