Charles Ellicott Commentary Genesis 35:20

"And Jacob set up a pillar upon her grave: the same is the Pillar of Rachel`s grave unto this day." — Genesis 35:20 (ASV)

That is the pillar of Rachel’s grave unto this day. —This is a later addition, but whether inserted by Moses or Ezra we cannot tell. Its site was known in the days of Samuel (1 Samuel 10:2); and as the pillar would be a mass of unwrought stone, with which the natives would have no object in interfering, its identification upon the conquest of Canaan would not be difficult.