Why do visitors leave pebbles on grave markers? For
years it was mainly a Jewish custom, but this shot is
from St. Michaels Cemetery in Wheaton, Illinois, a
Catholic grave yard.

One possiblility is that the practice dates back to
when graves were covered with rocks and stones to keep
animals from disturbing the remains. By leaving a stone
the visitor helped to maintain the grave. Another reason
might be to leave evidence that the person in the grave
is missed and being visited.

And this last one from a column in the Arizona Republic,
November 18, 2006: " In ancient times, shepherds would
keep track of how many sheep or goats were in their care
by carrying the equivalent number of pebbles in a pouch.
So a pebble on the headstone is a reminder that the
deceased is safe in God's care."