The Romans didn’t have that many limits. Ask the Christians who were used as torches at garden parties, or were wrapped in fresh animal skins and fed to hungry lions and bears, or the thousands crucified with spikes through their hands and feet. Or the gladiator shows. The Romans were hideously cruel.
You are looking at it through modern eyes. The Romans did not believe in equality or the humanity of those that they considered their inferiors. Most of those who were martyred were either slaves or plebs. They were fair game according the universal rules of the time.