Cahaba was a Prisoner of War camp where Union prisoners were held. After being released, the POWs were heading home to the States of Ohio, Indiana, Michigan, Tennessee, Kentucky, and West Virginia. They boarded the Sultana to take them home; there were survivors, but many died when the Sultana exploded in the Mississippi River.
River at Cahaba, Alabama
Cahaba Prison (Castle Morgan)
...the steamer "Sultana"...over 1,700 passengers [perished], mostly exchanged prisoners of war... . ...[there was] a terrific explosion (when the boiler burst)... .
She [the Sultana] was a regular St. Louis and New Orleans packet, and left the latter port on her fatal trip April 21, 1865, arriving at Vicksburg, Miss., with about two hundred passengers and crew on board.
...on board [were] 1,965 federal soldiers and 35 officers just released from the rebel prisons at Cahaba, Ala., Macon and Andersonville, Ga.... . Besides these there were two companies of infantry under arms, making a grand total of 2,300 souls on board, besides a number of mules and horses, and over one hundred hogsheads of sugar, the latter being in the hold of the boat and serving as ballast. [Source]