Lee's army was camped near Frederick on September 7. General J.E.B. Stuart's three cavalry brigades had been given the task of forming a screen (protective line) between the encampment and the Union Army to their east. Lee met with his generals suggesting to James Longstreet that he should surround Harpers Ferry Armory and attack the large Union garrison which was threatening their supply lines to their rear. Longstreet objected saying his troops needed rest from the long march. He also pointed out it was a bad idea to split Lee's forces when they were so close to the enemy. If the Union army discovered Lee had weakened his main force, they might attack in force. Once rested, organized and fully supplied, Lee's army could do what it wanted. After the meeting, Longstreet assumed Lee had given up the risky Harpers Ferry scheme. A day or two later, Longstreet entered Lee's tent. He found Lee and General Stonewall Jackson finalizing the plan to attack Harpers Ferry. Longstreet realized the plan had gone ahead without him. Reluctantly, he went along with the plan. On September 9, Lee wrote out the details of the plan in Special Order 191.