Origins of the Custom of Putting Stones on Graves When Visiting the Cemetery

Why Visitors Leave Stones on Grave Monuments - Jerry's Jewish Web Page

Whenever I go to visit someone's grave, I put a stone on top of it just before I leave. From Kolel: the Adult Centre for Liberal Jewish Learning

Why do Jews place stones on peoples' graves? From About

Gravesite Custom Has Desert Origin - Dear Abby

Rabbi Jonathan Maltzman of Kol Shalom Congregation relates the story of the Tradition of "Why Stones are Placed on the Grave." From Judean Gardens Cemetery

Jewish war veterans dead but not forgotten at Arlington

Why do we place stones on a grave when we visit? From Ask a Rabbi at Jewish.com

Why Do Jews Put Stones On Tombstones? From Jewish Virtual Library

Why put stones on graves?

Can somebody explain where the tradition of placing little stones on graves started? (Schindler's List has that towards the end of the Movie.) From Ohr Somayach