By the 1820s the residents of Edinburgh had taken to the streets to protest at the increase in grave robbing.[10] To avoid corpses being disinterred, bereaved families used several techniques in order to deter the thieves: guards were hired to watch the graves, and watchtowers were built in several cemeteries; some families hired a large stone slab that could be placed over a grave for a short period—until the body had begun to decay past the point of being useful for an anatomist. Other families used a mortsafe, an iron cage that surrounded the coffin.[11] The high levels of vigilance from the public, and the techniques used to deter the grave robbers, led to what the historian Ruth Richardson describes as "a growing atmosphere of crisis" among anatomists because of the shortage of corpses.[12] The historian Tim Marshall considers the situation meant "Burke and Hare took graverobbing to its logical conclusion: instead of digging up the dead, they accepted lucrative incentives to destroy the living".[13]