Just northeast, Maj. Gen. Joseph Hooker, commander of the Union Army of the Potomac, kept his headquarters from Jan. through June 1863 amid a vast city of tents and camps. There he rehabilitated the Union army after its catastrophic defeat in the First Battle of Fredericksburg in Dec. 1862 and its subsequent "Winter of Discontent." From there he designed a campaign to defeat Gen. Robert E. Lee's Army of Northern Virginia at Chancellorsville, a brilliant plan that failed in May 1863 because of his hesitancy and Lee's aggressiveness. President Abraham Lincoln visited Hooker there twice, in April 1863 and again in May after the defeat.