Mechanicsville, Battle of, June 26, 1862, first of the Seven Days' Battles in the American Civil War. It is also called the Battle of Beaver Dam Creek. Confederate forces of General Robert E. Lee attacked the exposed flank of General George B. McClellan's Union army, which was threatening Richmond, Virginia. “Stonewall” Jackson was late in aiding Lee, and the Union troops of General Fitz-John Porter's Fifth Corps held on until nightfall, then retreated to Gaines's Mill, where a second battle was fought.