What makes moral restraint in war possible? How have moral restraints been constructed and how – and why – have they changed over time? To what extent do such restraints actually restrain and what factors tend to shape this? This talk introduces a new project on the history of moral restraint in war. It starts from the premise that war and virtue stand in tension, that since wars must be fought, and won, it is not obvious or inevitable that soldiers and leaders would impose moral constraints on its conduct, constraints that might inhibit their capacity to win. The project takes a historical approach to the question, focusing not just on the ideas but on the practice of war as well. It begins – and this talk focuses on – the ancient Greeks, suggesting that the Greek world exhibited few constraints and identifying six central factors that might explain this. It is speculated that changes to the nature, content, and applicability of moral restraints can be traced to changes to these six factors beyond the Hellenistic period.