The Confederate forces opposing Sherman's advance were from the Department of Mississippi and East Louisiana, commanded by Lt. Gen. John C. Pemberton, a Pennsylvanian who chose to fight for the South. The officer in direct command of the defenses of Vicksburg was Maj. Gen. Martin L. Smith, who commanded four brigades led by Brig. Gens. Seth M. Barton, John C. Vaughn, John Gregg, and Edward D. Tracy. Brig. Gen. Stephen D. Lee commanded a provisional division with brigades commanded by Cols. William T. Withers and Allen Thomas; Lee was the primary commander of the Confederate defense in the Walnut Hills until the arrival late on December 29 of Maj. Gen. Carter L. Stevenson. Although the Union forces outnumbered the men to their front by two to one (30,720 to 13,792), they faced a formidable maze of both natural and man-made defenses. First was a thick entanglement of trees, which was broken intermittently by swampland. Chickasaw Bayou, a stream that was chest-deep, 50 yards wide, and choked with trees, also acted as a potential barrier to Sherman's men because it was parallel to the planned line of advance and could interrupt communication between units. Furthermore, the Confederates had formed dense barriers using felled trees for abatis.