... the adscripti operi were in a sense an integral part of the opus or works (the salt work or mine) and, when this was sold, passed together with their family into the service of the new master. Hence it was not a question of actual slavery, of chattel slavery, which allowed individual members of a family to be put on the market like any other commodity. The adscripti operi could marry and lead a genuine family life; they could own a minimum of property; and, naturally, they did not risk being killed with impunity: ‘their lives are under the protection of the laws of the land’. But it remained the case that in Scotland workers in coalmines and salt works were obliged to wear a collar on which the name of their master was inscribed.

— Liberalism by Domenico Losurdo (Page 67)