Like many top officers in the Civil War, both commanders of the opposing forces at Fort Sumter had fought on the same side in the Mexican War (1846-48).
P.G.T. Beauregard was the Confederate general who gave the order to fire on Fort Sumter on April 12, 1861, at 4:30 A.M., in the first battle of the Civil War.
His former comrade Robert Anderson surrendered the Union fort after withstanding bombardment for 34 hours.