The low earthworks opposite are the apex of the final Union line at Chancellorsville. After suffering defeat in the massive fighting on May 3, Hooker's army started digging. The result: a powerful, U-shaped line six miles long supported by 100 cannons, and made of "logs, knapsacks, dead horses, limber-chests and whatever came to hand." For two days Federal troops quietly held these works.
Despite the strength of the Union line, and despite having just 35,000 men on hand for action, Lee decided to attack the Union position on May 6. But Hooker never gave him the chance. On the night of May 5, the Union commander relinquished the virtually impregnable position and led his army back across the Rappahannock. It was perhaps his greatest mistake of the campaign.