In a cemetery, why do some tombstones have rocks on top of them?

Like this?

“The rocks left on top of the tombstone: an unexpected but completely logical feature. In Jewish tradition, small stones are left on top of the grave to honor the dead. Placing a pebble on Gertrude Stein’s grave reclaims her, in a sense, as a Jew, and I was glad to see that people have gotten into the habit of doing this. Proust, happily, gets the same treatment.”

Here (Just under half way down)

It means someone visited.

It is definitely a Jewish tradition, and these days it pretty much means exactly what @worriedguy says. When you visit, you leave a stone… kind of like a calling card.

It is a Jewish tradition. I’m not Jewish, but I do this when I visit the graves of my loved ones and my friends as a reminder that God is my rock, I remember you and this rememberance and love will not end. Even if it isn’t a grave of someone Jewish, Jews follow this tradition. It is a symbol of permanence.

Jewish tradition doesn’t usually use flowers. So the stone is left as a show of respect that you visited and that both you and the deceased are immortal. Even in death, you are not forgotten. It shows that you know the buriel site exists. The person is remembered with something solid.

Also, grave monuments use to be mounds of stones on top of the buriel site. Each person coming to the grave would leave a stone on the mound as a tribute, in a way, to the deceased.

Leaving a rock or a stone of a tombstone is a Jewish tradition. I am Jewish, and I always leave a rock or stone on a grave when I visit. This is so, because not only are rocks solid, but rocks NEVER die, unlike flowers. As a matter of fact, it is blatantly disrespectful to place flowers at a Jewish gravesite. Also, because rocks do not die, whereas flowers do…it is in Jewish tradition, that while the body dies, the soul does not, and also the memory of the deceased remains forever. Even, if I got ot a gravesite of someone who is gentile, I will place a rock on the tombstone, and no one is offended by this gesture

Leaving a rock on a tombstone is a Jewish tradition. Similar to leaving flowers. It means that they were there. It is derived from the fact that they were once Nomadic, and when someone died, they would bury them, then pile rocks on the body to prevent scavenger animals from digging it up.