Earlier quoted context omitted.
Under Roman law, the paterfamilias (i.e., the eldest adult male of the extended family) had the right to kill any other family member, at his pleasure. He could also control who (or even if) they married, sell them into slavery, etc.
"Over time, the absolute authority of the pater familias weakened, and rights that theoretically existed were no longer enforced or insisted upon. The power over life and death was abolished, the right of punishment was moderated and the sale of children was restricted to cases of extreme necessity. Under Emperor Hadrian, a father who killed his son was stripped of both his citizenship and all its attendant rights, h…
Hadrian was quite late in Roman history, far closer to its collapse than its founding.