The story of the Immortal 600 started with two Federal assaults on Battery Wagner outside Charleston, South Carolina. The second assault led by the famous 54th Massachusetts Infantry was gallant, but unsuccessful. Charleston was protected by Ft. Sumter, Battery Wagner and other gun emplacements. Charleston was a prize long sought by the Union forces. It was seen as the hotbed of secession. Frustrated by the failures against Battery Wagner, the Union commander, Gen. Quincy Gillmore decided to bombard the city of Charleston itself. Gillmore sent a note to the Confederate commander, Pierre G.T. Beauregard telling him to evacuate the defenses at Ft. Sumter and Battery Wagner and the other gun positions, or he would bombard the city. Charleston was three and four miles from its defenses, so there was no clear military target in the city. But, that was Gillmore’s plan. He threatened civilians, so as to force a withdrawal. Beauregard replied that shelling a defenseless city was barbaric, but he could not prevent the shelling. 
For the next several months, Gillmore’s batteries rained down projectiles on the defenseless city. In 1864, Gillmore was replaced as commander by Gen. John G. Foster. Beauregard was replaced, by Gen. Samuel Jones. Jones complained to Foster that his cannon were deliberately targeting non-military sites. Jones placed 50 captured Union officers in a house in downtown Charleston. Few of the Union shells landed near the house, but still, the Federals were not happy. Gen. Foster then requested an equal number of captured Confederate officers to be placed near the Union fort on Morris Island. 
Upon hearing of Foster’s request, five of the Union officers housed at the house in downtown Charleston, all captured general officers, sent a letter to Gen. Foster asking that Confederate officers be treated humanely, as they had been treated. In truth, the 50 Federal officers kept at the Charleston house lived well. As one Charlestonian remarked, the Federal prisoners had a large lot in which to walk around. The Confederate government installed gas lighting for the prisoners. The captured officers received many visitors and were a well-dressed lot. They had money to spend. They were all on parole, meaning they were restrained only by their word. There was one guard, but the prisoners had a great deal of freedom. They could buy sugar and coffee in the city, despite severe shortages. Local citizens would call on them and visit. 
The Parole System
Officer POW’s well into the Civil War could enjoy a substantial amount of freedom while on parole. That was part of a long-standing tradition. During the Napoleonic wars, it was common for captured British officers to enjoy the freedom of Paris, so long as their family could send them money. The captured British officers during the European wars simply had to swear an oath that they would not try to escape and then the freedom of the city was theirs. The captured Union officers enjoyed a similar level of freedom, likely because their families could send them money.
Gen. Foster obtained his 50 Confederate officers. But, they were soon exchanged for the 50 original Federal officers at the house in downtown Charleston. 
Later, in late summer of 1864, Confederate Gen. Jones was forced to accept a large number of Federal officers from the POW camp at Andersonville, Georgia. The Union POW’s were placed at Roper Hospital and the city jail in Charleston and in various houses in Charleston. Gen. Jones wrote to Gen. Wessels, one of the original captured 50 officers that he was sorry about having to place so many Federal officers in the city, but it was the only secure place where they could be guarded until they were moved to a more permanent location. 
In August, 1864, Federal Gen. Foster wrote to his superior that he knew the large number of officers were placed in Charleston while enroute to somewhere else, not with the intent to expose them to enemy artillery. Foster also stated that he knew the original 50 federal officers were safe, because he knew where they were and his gunners would avoid that area. 
Yet, Gen. Foster still requested 600 confederate officer prisoners. He planned to place them adjacent to the Union guns on Morris Island, directly in the line of fire.
 Karen Stokes, The Immortal 600 (Charleston, SC: History Press 2015), p. 35-36
 Stokes, Immortal 600, p. 36-37
 Stokes, Immortal 600, p. 39-43
 Stokes, Immortal 600, p. 43
 Stokes, Immortal 600, p. 43-46