Two men named Robert Prine lived in Mississippi when the Civil War began. The one from Marion County enlisted in Co "F", 7th Mississippi Regt, serving for a short period of time. John L Prine is the only man by that name in either the 17th Mississippi Cavalry Battn or the 9th Mississippi Cavalry. Don't know where the memorial information may have originated, but it has to be called into question.
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=24886582