In June 1863, Harrisburg braced for an invasion. The Confederate troops of Lieutenant General Richard S. Ewell steadily moved toward the Pennsylvania capital. Capturing Carlisle en route, Ewell sent forth a brigade of cavalry under Brigadier General Albert Gallatin Jenkins. After occupying Mechanicsburg for two days, Jenkins's troops skirmished with Union militia near Harrisburg. Jenkins then reported back to Ewell that Harrisburg was vulnerable. Ewell, however, received orders from army commander Lee to concentrate southward--toward Gettysburg--immediately. Left in front of Harrisburg,...