A coin left on a headstone or at the grave site is meant as a message to the deceased soldier's family that someone else has visited the grave to pay respect. Leaving a penny at the grave means simply that you visited. A nickel indicates that you and the deceased trained at boot camp together, while a dime means you served with him in some capacity. By leaving a quarter at the grave, you are telling the family that you were with the solider when he was killed. According to tradition, the money left at graves in national cemeteries and state veterans cemeteries is eventually collected, and the funds are put toward maintaining the cemetery or paying burial costs for indigent veterans.
The tradition of leaving coins on the headstones of military men and women can be traced to as far back as the Roman empire. The custom has its roots in the ancient Greco-Roman belief that anyone who died would need money to pay Charon, the ferryman who would transport them across the River Styx to the underworld.
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