Yet it is probable that ordinary labour in towns was conducted on a system like that introduced by Diocletian, whereby the labourer was bound to pursue an hereditary calling, but received wages and provided his own keep. This is the system indicated in the tenth-century "Book of the Prefect". The "Farmer's Law" of the seventh and eighth centuries shows the free "colonus" working in his village, and the slave working on the large landed proprietor's estate, but both classes tended to fall into the condition of serfs tied to the soil.