Fort Monroe ( a.k.a. Fortress Monroe) is a Hampton VA military installation located at the tip of the Virginia Peninsula. Although most of Virginia became part of the Confederate States of America, Fort Monroe remained in Union hands.
As Petersburg fell, Richmond was evacuated in 1865 and President Davis escaped, only to be captured in Irwinville GA. He was sent to Fort Monroe and confined to an unheated open casement until the Union Surgeon John J. Craven recommended more humane care for Mr. Davis. He was held there for two years and some historians have speculated that his treatment in captivity was intended to be lethal.
In poor health, Davis was released in May 1867 on bail, which was posted by prominent citizens including Horace Greeley and Cornelius Vanderbilt who had become convinced he was being treated unfairly. The federal government proceeded no further in its prosecution due to the constitutional concerns of U.S. Supreme Court Chief Justice Salmon P. Chase.
One of several books about Fort Monroe is "Defender of the Chesapeake". Yesterday I mentioned Andersonville Prison. One of the books about that dreadful place is titled "Tragedy of Libby and Andersonville Prison Camps" in case you want to read more on the subject of Civil War prisons.