There is a much quoted statistic about contemporary war. At the beginning of the twentieth century 90 per cent of casualties were soldiers. In today's conflicts, 90 per cent of the dead and wounded are civilians.

These figures are striking, but it is a mistake, as Hugo Slim demonstrates in Killing Civilians, to think that noncombatants have ever been anything but extremely vulnerable. The moments in history when they were actually safe in wartime were only ‘blips’ in humanity's ‘long and bloody history of conquest, group rivalry, religious fanaticism, political extremism, empire building and modern state formation’. Moving backwards and forwards across time, Slim charts the many depressing ways in which, from the start of recorded time, civilians have been harried, displaced, imprisoned, hounded, tortured, raped, mutilated and massacred as part of warfare. As the historian R J Rummel notes, in the twentieth century alone an estimated 217 million people died, and countless others were injured as a result of war.

Running parallel to this story of affliction are the attempts that have been made to protect those not directly involved in warfare. Medieval historians distinguished between armed and unarmed populations, using the Latin word innocens – not capable of harming – to denote individuals who were entitled to protection (though