Q: Will you please explain the symbolism of placing stones on tombstones?
-- C. Lewis

A: The practice of burying the dead with flowers is almost as old as humanity. Even in prehistoric caves, some burial grounds have been found with evidence that flowers were used in interment. But Jewish authorities have often objected to bringing flowers to the grave. There are scattered Talmudic mentions of spices and twigs used in burial (Berachot 43a, Betzah 6a). Yet the prevailing view was that bringing flowers smacks of a pagan custom.

That is why, today, one rarely sees flowers on the graves in traditional Jewish cemeteries. Instead there are stones, small and large, piled without pattern on the grave, as though a community were being haphazardly built. Walking in the military cemetery of Jerusalem, for example, one can see heaps of stones on the graves of fallen soldiers, like small fortresses.

For many of us, stones conjure a harsh image. It does not seem the appropriate memorial for one who has died.

But stones have a special significance in Judaism. In the Bible, an altar -- the holy place where one offers to God -- is no more than a pile of stones. When Abraham, following God's instructions, binds his son Isaac for sacrifice, he does this at a stone, called Even Hashtiyah, the "foundation stone of the world." And the most sacred shrine in Judaism, after all, is a pile of stones -- the wall of the second Temple.

So stones have special meaning. But why place stones on the grave? The explanations vary, from the superstitious to the poignant.

There is a belief, with roots in the Talmud, that souls continue to dwell for a while in the graves in which they are placed. In the Eastern European folk imagination, these souls -- even those that were benign in life -- can take on a certain terror in death. The stories of Isaac Bashevis Singer and the plays of the Yiddish theatre, rich in the mythology of Eastern European Jewry, are filled with these types of hauntings: souls who returned, for whatever reason, to the world of the living.

The practice of leaving stones atop a grave can be explained as a response to these beliefs. More than a simple marker of one's visit, stones on the grave are the means by which the living help souls remain where they belong -- in the grave where they do no haunting.

Another beautiful answer to the stones on graves question takes its cue from the inscription on many gravestones: the five-letter Hebrew abbreviation taf, nun, tsadi, bet, hey, which stands for "teheye nishmato tsrurah b'tsror haChayyim." This phrase is usually translated as "May his soul be bound up in the bounds of eternal life" -- a phrase wishing for eternal life for the departed.

Yet tsror (the fourth word of the Hebrew phrase) can also be translated as "pebble." Suddenly, the phrase takes on a more nuanced meaning, based on the historical significance of pebbles.

In ancient times, shepherds needed a system to keep track of their flocks. On some days, they would go out to pasture with a flock of thirty; on other days a flock of ten; the third day with fifty. As memory was an unreliable way of keeping tabs on the number of the flock that day, the shepherd would carry a sling over his shoulder, and in it keep the number of tsror, pebbles, that corresponded to the number in his flock. That way he could have an accurate daily count.

When we place stones on the grave, and inscribe the motto above on the stone, we are asking God to keep the departed's soul in God's sling. Among all the souls whom God has to watch over, we wish to add the name, the "pebble" of the soul of our departed.

One thing both of these explanations have in common is the sense of solidity that stones give. Flowers are a good metaphor for life. Life withers; it fades like a flower. As Isaiah says "All flesh is grass, and all its beauty like the flower of the field; grass withers and flowers fade" (Isaiah 40:6,7). For that reason, flowers are an apt symbol of passing.

But memory is supposed to be lasting. While flowers may be a good metaphor for the brevity of life, stones seem better suited to the permanence of memory. Stones do not die.

There is something suiting the antiquity and solidity of Judaism in the symbol of a stone. In moments when we are reminded of the fragility of life, Judaism reminds us that there is permanence amid the pain. While other things fade, stones and souls endure.