David, it is well documented (e.g. To Live and Die in Chicago...) that the Lincoln administration had a policy towards mistreatment of Confederate POW's that included withholding available fresh fruit and vegetables necessary to avoid dreadful diseases. These same people played up Andersonville very well. At Camp Douglas, the prison commanders were too lazy and careless to even keep up with the identities of dead soldiers, so there may be over 2,000 unaccounted. No, it does not surprise me at all that your ggg-grandfather's grave was left unmarked even thought they knew of him. It is a small comfort to me that citizens in Chicago were very sympathetic to the plight of Confederate prisoners and some risked their livelihoods and freedom to aid them. Perhaps that was the situation where your grandfather lived his last days. All wrongs are made right in the next world.