Leaving stone when visiting grave

We know there is a common custom to leave a little stone/rock on top of a grave when one visits a grave at the cemetery. 1) What is the source of this custom? 2) Are you allowed to clear off stones when they become a big pile or if you want to clean the tombstone? Thank you

Shalom!

Thank you for your question.

First a word on tombstones in general.

The Jewish origins of mounting a tombstone on a grave likely comes from Yakov Avinu who mounted a tombstone on the grave of Rachel. There is even a view that mounting a tombstone on a grave is a Torah obligation, while others hold that it is a rabbinic requirement. In fact, one is not permitted to forego a tombstone upon one’s grave, and any such requests are to be ignored. In any event, it is a Jewish requirement. To further highlight the importance of a tombstone, the Talmud calls it a “nefesh” meaning “soul” as if to say the soul of the deceased is connected to the tombstone. We are told that the soul of the deceased derives pleasure by having a tombstone in its grave

One reason for the important of a tombstone is that it informs visitors who is buried there and allows them to pray and pay their respects. In ancient times, when graves were sometimes placed at random, the tombstone served to convey to Kohanim that there is a deceased in the area and that they should keep away.

There are a number of customs that are followed when visiting a grave. One such custom is to touch the tombstone with one’s left hand. As you mention, it is also customary to put a small stone on the grave or tombstone, as well. This is in order to convey to family and passersby that people have visited the grave. If the stones overly pile up, it is permitted to remove them and they have no sanctity. Indeed, they should be removed if they are covering up the name and other details of the deceased.

Bereishit 35:20; Moed Katan 5b;  Nidda 57a; Rambam, Hilchot Avel 4:4;  Sefer Chassidim 738