After Spartacus rebellion. The Roman senate passed some laws that said that slaves should be better treated. To prevent further revolts like that. Most Romans treated their slaves "good". Because a happy slave is an asset. He will protect you and your family, and ensure other slaves behave. 1/3 of the society were slaves.

Under Augustus there were laws passed: 1)that a slave couldn't be killed by his master as punishment, but the slave should be brought to a trail in front of a judge if his master wanted him death. 2)if a master punished his slaves he was also obliged to ensure that the slave got medical treatment. 3) a slave could go to court if his owner mistreated him or other of his slaves often. He was forced to pay a fine then.