For those families who could not afford a durable inscription, the passage of time would have brought considerable anxiety, as such grave markers as they could provide gradually eroded, shifted or were displaced, with the grave's exact location, and the identity of the deceased, lost as the cemetery gradually filled. Many would have received no marker or epitaph at all; most of Rome's slaves were "servi rustici", used for agricultural labour. Few (if any) had the opportunities afforded to many urban household slaves, to buy their freedom with money earned and a promise of future favours. Almost all would have been enslaved for the whole of their lives, "and it is thought that they practically never appear in the epigraphic (or any other) record."