A common misconception is that Romans regarded their slaves as “things”, chattels that could be sold and dealt with in any way the master saw fit. This is not correct. Gaius states in his Institutes (Bk 1:8 & 9) that the primary division of the law of persons is that men are either free or slaves. This must surely mean that slaves were for the purposes of Roman law dealt with as “persons”, not as things.
Furthermore, a slave who had been manumitted (= freed by way of an act of manumission, literally: "sent from the hand"), and who had not been branded by some disgrace, became a Roman citizen upon being so freed. This would not have been possible if he had been regarded as a thing.
In principle, a Roman paterfamilias (male head of the family, literally: father of the family) had what was called the ius vitae necisque (= the right of life and death) over everyone who fell under his patrimony, including his wife and children. In ancient times this practically meant he could kill anyone falling within his patria potestas (the power of the father). Obviously this remedy was one that was (as far as we know) not often resorted to, and certainly in later times slaves were regarded as worthy of special protection.
Even if slaves were valuable “assets” in Roman society, legislation, as least from the time of the emperor Antoninus Pius (reigned 138 CE – 161 CE) curbed excessive severity to and killing of even one’s own slaves without justifiable cause, by rendering them liable to the same extent as if the slave had belonged to another person. If a master was found to be intolerably harsh to his slave(s), he could even be forced to sell his slave(s). The same kind of protection was not available to the free members of a paterfamilias’ household, even if in practice the paterfamilias rarely would exercise his right of life and death.
Having said that, it does not mean that slaves were necessarily treated on an equal footing as the rest of the household, although in most Roman households, the slaves were regarded as part of the household and treated fairly well. It became the usage to free especially older slaves upon the death of the paterfamilias, conferring upon such freed slaves sufficient money to either set themselves up in business, or to live their last days in peace and quiet.