It's an iron fist? But topaz is much harder than iron. Don't these people know their Mohs scale of mineral hardness? Regardless, the Romans couldn't do this because their whole identity was wrapped up in an idea of justice that precluded indiscriminate violence. The other strategy is to try to incorporate conquered people into the empire more fully, in Rome's case, to make them Romans. This worked really well in the early days of the Roman Republic, and even at the beginning of the empire, but it eventually led to barbarians inside the gates. The decline of the Roman legion started long before Rome started getting sacked.