Origin of "Giving Someone The Sack"

¿Why do we say we've been given the sack when we are fired from a job?.
This expression was first recorded in 17th century France. It is thought to date back to days when workmen carried their tools around from job to job in a bag (sac in French). When the job was finished they would have to pick up their bag an leave, hence the idea of being given the "sack".